None of this is in any way official, or the “One, True Way” or anything like that, but it is my best attempt to distill my skills for new ’brewers. I have made a lot of classes, and my work was enough to get me noticed by Rule of Cool gaming, and my name now appears as a design credit in their system, Legend. What follows is a somewhat-rambling discourse on some of the things I’ve gleaned from my time homebrewing. They remain the best suggestions anyone can give you, but some specifics about classes in 3.5 seem appropriate. However, those are both really general suggestions, and probably apply to just about any endeavor out there. Stuff made in a vacuum is rarely good I know this to be true even of my own work. Homebrewing takes experience and it takes feedback. There are a lot of forums dedicated to roleplaying games, and a lot of them have a lot of veteran 3.5 players, and a lot of them have dedicated homebrew forums. My #1 suggestion, though, is to put your work out there.
Even stuff about non-role-playing game design can provide good insights.
There’s a lot of material out there about class design, both specific to Dungeons & Dragons 3.5 and to games in general.