The first step to keeping things simple is to just use the stuff you need and want and ignore the rest. This is actually encouraged by the game designers and easy to do with the modular concept.
This page will link to a bunch of "How to" type posts and supplements. Lets start with...
How to be a GURPS GM
- How to be a GURPS GM: This is a solid overview of running GURPS and a good help for any GM. If your experienced with GURPS you still may pick up some pointers.
- How to be a GURPS GM: Managing Expectations: Advice for setting expectations for the campaign. Useful for other systems too actually. This supplement helps a GM figure out and set the expectations in a way that helps everyone have more fun.
- How to be a GURPS GM: Ritual Path Magic: Ritual Path Magic is a magic system for GURPS first seen in the GURPS Monster Hunters line. It is a powerful flexible system designed to emulate the genre and fiction such as Buffy the Vampire Slayer and the Dresden Files. However while the magic in those stories is controlled by plot this system can bog down a game or make things too easy. This supplement helps you understand the system and take advantage of its drawbacks. Also offers suggestions and rules for speeding things up in play. You'll need GURPS Thaumatology: Ritual Path Magic for this to be useful