Philosophy Behind Advancing Your Heroes
Advancing your Heroes is not as simple as raising their stats in some way. There is quite a bit for you, the Game Master, to think about before you allow the Heroes to do so, during the game, and after the quest is completed. Allowing the Heroes to advance can give them a goal to work towards, and a feeling of accomplishment when the goal is achieved. The thoughts below were written for my system of advancement, but can be applied to any system that you use.
The first thing that you have to decide on is the cost. The figures I gave are really just guidelines. You will have to decide yourself how much to charge the Heroes to raise a stat, study in a spell college, or learn a new spell. If you make the cost too low, the Heroes will be advancing too much and will not get the sense of accomplishing something difficult that they should. On the other hand raising the cost too high will discourage the Heroes. A good rule of thumb is to allow a Hero to raise a stat about every 30-40 quest levels played. You may want to change this depending on your players, but you should pick a number of quests played per stat advancement. See if your players are training at this level you have set. If not, you may need to adjust the cost.
The second thing you need to work on is the rewards given during a quest. If your Heroes are getting huge amounts of gold, or are able to keep all the gold they find without buying supplies, then you may reduce the amount of gold the Heroes are given during the quest or for completing the quest. Likewise if the Heroes are finishing quest packs without seeming to gain anything monetary wise, and are using all the gold they find to buy supplies, you may need to raise the amount they find. Changing the amount of gold found in treasure chests or as a reward for completing the quest is an alternative to changing the price for training.
One of the biggest things you need to do when your Heroes are raising their stat levels is to make the quests harder. While an occasional easy level can be fun, if every level is too easy for the Heroes the game will quickly loose its interest. There are two ways you can make a quest harder. One is to add more monsters into a room. If a room has 4 Goblins, add one or two more. If a room has three Zombies, add a Mummy and/or a couple of Skeletons. The second way is to purchase some new figures. Make these figures have harder stats than those that came with the basic HeroQuest game. This will give the Heroes a challenge after they have raised their levels. Be careful about introducing harder monsters too quickly, though. When you first begin allowing the Heroes to advance, after one of the Heroes has raised his Body Point once is not the time to introduce a Horde of Dragons, each with 15 Body Points. Bring in the new monsters at the proper time.