I want to learn preamp/pickup installation

Seymour Duncan has a series of blog posts :
Guitar Wiring Diploma Course - Guitar Pickups, Bass Pickups, Pedals

Other than that, read lots of diagrams, increase in complexity over time, think in terms of chained and sequential modules as much as possible, and have fun

 

Fralin has (or, had) a blog with a lot of wiring articles on it as well.

And if you want to get in to YouTube, Stewmac makes a lot of great videos for repair and modification techniques. Their products tend to have good instructions as well, which are all on their website.

Generally, when it comes to active preamps, the wiring is basically a matter of following the manufacturer's directions. There's not really much in the way of general best practice or standards, at least as compared to wiring passive instruments. The best way to learn about installing active EQs is probably to just look at manufacturer instructions.

 

Do you mean building your own preamp or just installing a pre-built unit into an instrument? If you want to understand and build a preamp, here's an easy introduction made by TB'er @RobbieK- in fact he has a number of great videos that can teach you some valuable basics via demonstrations of mods, repairs and builds he has done filmed and explained in real-time.
For more of the theory and projects another good intro would be the old book
Electronic Projects for Musicians, A Comprehensive Guide
by Craig Anderton:
Electronic Projects for Musicians, A Comprehensive Guide | Amplified Parts