Look on Amazon for Peter Riddle's books. Some are out of print and tend to get pricy, but he knows his stuff.

I agree about Peter Riddle, this is a pretty good one, it's current and reasonably priced. It will cover all the basics of layout wiring. 

If you have DCS, get The DCS O gauge Companion (Barry's book) Covers DCS system and DCS specific wiring.

You didn't mention what kind of layout you are wiring.  Is it a modern layout or a postwar or earlier layout?

I would follow the wiring instructions in Barry Broskowitz's book "The DCS O Gauge Companion".  You can find a link to buying it on the DCS forum page.

This wiring scheme works for all conventional and command control configurations.  You may want to add command control later even if you don't have it now.

I have wired two layouts using this method with no problems.    Both layouts have crossovers and double slip switches.  Both layouts have isolated loops.  I plan to install modern MTH crossing signals on one layout following the instructions that came with the signals.  I also use Stuff sensors to activate signals and accessories.  Again, I following the wiring diagram provided by the manufacturer.  

Your crossing signal and double crossover should come with wiring instructions.  I am sure that you can probably find wiring instructions for older Lionel crossing signals online.

Joe