The wiki is your friend for the most part so don't be afraid to use it
The primary mod in the pack is undoubtedly Thermal Expansion 3, which handles pretty much everything from power generation to materials processing and routing. I'd advise playing around with that a bit and then moving on to things like Buildcraft quarries for mining, Applied Energistics for storage and crafting, and Big Reactors for large scale power generation.
You won't find much in the way of guides for Tekkit in general so you need to just get the hang of specific mods in the pack. If you're looking for mod guides I highly recommend the Mindcrafters. There's another group out there too but I can't seem to recall it for the life of me so I'm sure someone will post it up.