This is a very simple thing to do, but almost all of us do it, the boar gives an amazing amount of food early.
http://homepage.ntlworld.com/walbanger/Pages/HelpBoar.htm

Simple, but I've actually based my play around remembering these things;
http://homepage.ntlworld.com/walbanger/Pages/HelpBasics.htm

Very important Economy things are often forgotten
http://homepage.ntlworld.com/walbanger/Pages/HelpEconomy.htm

Simple useful tips;
http://aok.heavengames.com/cgi-bin/aokcgi/display.cgi?action=ct&f=3,28233,1,10

How not to suck; simple guide:
http://www.reddit.com/r/aoe2/comments/1c7zwe/how_to_not_suck_at_aoe2/

This guy knows what he's talking about;
http://zeroempires.net/effective-booming/