You should be able to find some in-depth strategies and build-orders online, but I'll give a short overview of what I remember:

Ra is terrible at fighting in the classical age, but really picks up in heroic and mythic. A common strategy is called a "fast heroic", where you aim to get into the heroic age ASAP and get a midgol stronghold up. Rain is commonly used to provide a large food boost in order to have enough to advance.

Ra is good at booming. Almost always you should be improving your economy and building cheap buildings to gain map control.

> and how do I play to his strengths late-game?

Out-boom your opponent. Having 3+ town centers and a ton of empowered caravans is extremely important. Ra tends to be cheap in the late game - spam catapults, rocs, elephants, ballista towers, walls, and so on. If you boom to much then go for a wonder. 

Much more in-depth guides:

http://www.rts-sanctuary.com/RTS-Sanctuary/showtopic=41938

http://aom.heavengames.com/cgi-bin/forums/display.cgi?action=ct&f=1,26431,0,all

http://aom.heavengames.com/cgi-bin/forums/display.cgi?action=ct&f=1,28266,0,all