I don't really need tips on building effective characters, per se. This may be something suited for beginners, but even then, I wonder about the actual need for such sections. It almost always is the least interesting part of the book for me.
I like having new feats, and I like having new prestige classes. I wonder about playtesting, though. I have no insight into how well they are tested, but sometimes I wonder if any were tested at all. I'd much rather have 4 or 5 solid, very different or original prestige classes in a class book than 20 prestige classes of varying quality. I think a section on how to design prestige classes for the various character types may be more useful in a class book than the DMG alone. For example, instead of giving us 5 PrC's which each focus on fighters using a specialized type of weapon (The Lasher, Master of Chains, Weaponmaster, etc.), why not show DMs how to build a weapon-specialized fighter with a step by step process or something along those lines.
New equipment, spells, magic items, etc. are great as well. Rules on creating new spells, or a new weapon would be even better.
I like having new feats, and I like having new prestige classes. I wonder about playtesting, though. I have no insight into how well they are tested, but sometimes I wonder if any were tested at all. I'd much rather have 4 or 5 solid, very different or original prestige classes in a class book than 20 prestige classes of varying quality. I think a section on how to design prestige classes for the various character types may be more useful in a class book than the DMG alone. For example, instead of giving us 5 PrC's which each focus on fighters using a specialized type of weapon (The Lasher, Master of Chains, Weaponmaster, etc.), why not show DMs how to build a weapon-specialized fighter with a step by step process or something along those lines.
New equipment, spells, magic items, etc. are great as well. Rules on creating new spells, or a new weapon would be even better.