Below are a list of documents and websites that are worth investigating to improve your referee skills:

Players Equipment
For a quick resource on what can and cannot be worn on the field, see the AYSO Wiki. This information is also Chapter 2 of the AYSO Reference Book, referenced above. 

National Rules and Regulations
The AYSO Referee Guideline is updated annually and written specifically for AYSO Referees. It answers many AYSO-specific rules not covered by the IFAB Laws but are important to AYSO 10U games (no drop kicks, build-out line, etc.). You can also find rules related to player equipment (casts/splints, hair beads, etc.). Chapter 2 of the AYSO Reference Book is the National Rules and Regulations and has similar information. 

Laws of the Game (IFAB)
IFAB Laws of the Game – English
The Laws of the Game App

(EVERY REFEREE SHOULD HAVE THIS ON THEIR SMARTPHONE)
IFAB Laws of the Game - Apple
IFAB Laws of the Game - Android

The Referee section of FIFA.com
FIFA Refereeing

The Referee section of USSF
https://www.ussoccer.com/referee-program

Ask The Ref – There is a large forum with user submitted questions that are answered by experienced referees.  Just about any question you can imagine has been asked and replied to already.  This is a great source of information if you have a question regarding a specific in-game scenario. http://www.asktheref.com/

Facebook group providing support and guidance to female AYSO referees
https://www.facebook.com/groups/622428462075997/?ref=share