Mistakes from a mechanics point of view
Telling people to turn to the wrong paragraph
This can cause the game to grind to a halt. You tell the reader to turn to paragraph x, but paragraph x makes no sense. Where do you go now? I suppose the only solution is to search for a paragraph that makes sense and this involves going through the book which can be a long tedious process.
Solution: using ADVELH or another gamebook program could sort this out. If you do not use a program, then you may have to double check by reading through every possible path.
Giving people the wrong stats
Example: Triad of skulls
In the triad of skulls, I told the player to roll 1 die (d6) and add 9 for their skill, giving the hero a skill of 10-15. I intended to say roll one die and divide the result by 2, rounding fractions up and add 9, giving a skill of 10-12. Anyone who played it with a skill of 13-15 probably found the gamebook far too easy. This was a schoolboy error.
Solution: Even if you don't proofread the whole book, at least proofread the important stuff, like stat determination.
Not following your own rules
Example: Creature of Havoc
I Creature of Havoc, you need to find a magic pendant that can find secret doors. When you see the phrase, 'You cannot see a thing...', you follow the instructions in the book to turn to a new paragraph. Later you are told to do this when you read 'You find yourself...'. However, paragraph 213 does not start with either of these phrases but you still have to follow the instructions for the pendant. There is a case that this is quite an inspired decision but it must have caused a lot of frustration. For more information on this mistake and for a walkthrough, click here.
Solution: Doing a playtest.
Not considering all possibilities
Example: Creature of Havoc (again, sorry - it really is a good gamebook)
Despite Creature of Havoc being one of the most difficult gamebooks ever, the fights are actually very easy to win. Damage against you in combat is reduced and you automatically kill your opponent if you roll a double on 2d6 (which means that you have a 1 in 6 chance of killing an opponent each round).
You may get into a combat with Thugruff, a half troll. If you reduce his stamina to 4 or less, he calls his army which kills you. However, there is no paragraph to turn to if you kill him automatically. You may have been able to escape if you did that.
Solution: When you write combats and situations have all rules in mind. The above example just needed an extra paragraph saying what happened if you kill Thugruff. It would have been fine if it was another instant death for you as long as it had been considered.
Having decisions which make future decisions impossible
Example: Revenge of the Vampire
In revenge of the paper, you can buy a horse to pursue something at the beginning of the book. You can only buy the horse if you have at least 8 gold pieces and it costs all of your money. You later come to an inn where you have to pay money to stay there. Except you can't because you spent all of your money and you can't get to that part if you don't buy the horse.
Having stat changes that are ambiguous
Example: Talisman of Death (but there are others)
Skill bonuses are ambiguous in early Fighting Fantasy books. When you get a magical weapon or piece of magical armour, you are told to increase your skill. However, you are told in the rules that your skill cannot go above its initial value so if your skill is at its maximum, the bonus is lost.
Talisman of Death does this a lot. You can get some chainmail armour, a spear, a ring and a helmet that increases your skill. From the description in the text, it sounds like it should take your skill over its initial value. The helmet bestows quickness of thought on the wearer. The ring is a ring of skill at arms. The chainmail and spear is magical. However, if you follow the rules, then you cannot use them to go over your initial skill.
Also, you might lose your sword in Talisman of Death, reducing your skill by 2 points. What happens if you drink a potion of skill (restoring it to its initial value) and then get another sword. Does increase your skill?
Solution: In the above example, the solution is to modify attack strength rather than skill. One way to get a round this is to ask someone else to read the rules and see if they can understand them from what we have written as we are sometimes too 'immersed' in our own creations to see their flaws.
Having infinite loops
Example: Fabled Lands
In the above example, you could fight an infinite number of muggers and get 15 shards each time or go to a part of the hills an infinite number of times where you might just increase a stat. This means that if readers are prepared to exploit these infinite loops, then they can break the game.
Soution: Playtesting. Find someone who likes breaking games and exploiting bugs and get them to playtest it.
Making the gamebook impossible
Example: Crypt of the Sorcerer
Razaak is a skill 12 stamina 20 opponent who kills you if he scores two consecutive hits. There are plenty more difficult battles so winning it fairly is almost impossible. Your gamebook may also be impossible if you have missed out a vital item or told the hero to turn to a different paragraph.
Solution: Reduce your opponents' stats or increase your stats. Playtesting.
Mistakes from a story point of view
Having a decision which is not acknowledged by the text
Example: Talisman of Death (again, sorry. It was my first gamebook so I love it).
This is by no means a gamebreaker but it could break the suspension of disbelief. In Talisman of Death, you may end up fighting a cut throat and two other thieves. If you kill one thief (not the cut throat) and wound another then the fight ends. The paragraph states that the cut throat yields. However, you may have killed the cut throat in combat.
Solution: Make sure that the story covers all possibilities. In the above case, leave out what the cut throat did as you don't know if he was alive or dead or you could say that you have to kill the cut throat.
Lack of consistency with items or characters
Example: Return to Firetop Mountain
In Return to Firetop Mountain, you could find a bronze tooth with a flame on it. Later on, it is described as a silver tooth with a number on.
So it seems that most of the solutions are proofreading or playtesting (it is also best to get someone else to do it as it is harder to see our own mistakes. We are too familiar with the work and our brains cover up the mistakes with what we think we wrote).
Since Playtesting is needed, I have copied something about Playtesting from the Official Fighting Fantasy website's How to Write a Gamebook series.
Steve: After the text had been written, the numerical references had to be randomised. Ian and I had two approaches to this. Probably his way was better. He used to have a sheet with the numbers 1-400 written down. As he wrote a reference he would pick a number from the sheet and cross it off. So when all 400 numbers had been allocated, the book was finished! I used an alphanumeric system. Each of the (let’s say) 30 main encounters was given a number from 1-30. When I came to write the encounter up, all the sub-paragraphs were given letters. Perhaps 15A was the start of an encounter with the Ganjees. From this there would be various options and each option was given another letter, perhaps 15B, C or D. There were further sub- paragraphs from these, and sometimes I’d find I was numbering a paragraph as ‘25C (iii) a’. Very confusing to an outsider, I’m sure. But I knew what was going on. I liked this method because whilst the book was being written I could always tell at a glance where a reference came from (“If it’s 15-something it’s from the Ganjees” etc). But the downside was that I’d have to go through and re-number everything at a later stage. Plus I didn’t have any instant total of the references I’d written. In the end this resulted in me abandoning the 400-reference standard. Only Warlock, Citadel and House of Hell had exactly 400.
My re-numbering process was the most tedious part of writing the book. I used two sheets of paper, one with the numbers 1-400 on and the other with a listing of all my alphanumeric references. It was then necessary to go through and replace each alphanumeric reference with a 1-400 reference. All the time this was being done you had to bear in mind that the paragraphs to be illustrated had to be spaced equally apart, otherwise you might have two illustrated paragraphs on the same page of the book. And once the final codes had been allocated, there was maybe a week’s work in checking and re-checking all the numbered references matched up properly. Finally, after months of work, the manuscript would be ready to be delivered to the publishers. But in between delivery and publication there was more work to do. In those days, the author’s typewritten manuscript would be re-typed by a typesetter, resulting in long pages of text known as ‘galleys’ that had to be checked for typos and numbering errors. Finally ‘page proofs’ would arrive – all the text and the illustrations set out ready to paste up into the final pages as they would appear in the book.
Jon: By trying to ensure that there is a balance in the book between opportunities to recover points for the player's various attributes along with the chances to lose them. I know I have been criticised in the past for having too many powerful enemies but in the books there are plenty of opportunities to gain items or abilities which can lend you an advantage. However, I think I have achieved this most successfully in 'Bloodbones'.