The sooner you put points in retribution, the sooner you get the fun stuff: Seal of Command, Crusader Strike, Judgements of the Wise, Divine Storm. This is where i'd put the points up to around level 43:
http://www.wowhead.com/?talent=sZZVf0tbIuc0c
Once you have the required points for Judgements of the Wise (i.e, infinite mana) you can respec to put the 5 points from Benediction to Deflection. Which will mitigate some more damage resulting in less downtime, and also parrying cuts some time off your next auto-swing and so is a small damage increase. Then just move down the ret tree until Divine Storm.
Ignore Improved Blessing of Might and Divine Strength until close to lv 80. At level 20 or so, they'll give you an increase of perhaps 25 attack power which isn't remotely noticable. As your gear improves, Divine Strength becomes more effective, and as you get more powerful ranks of Blessing of Might the talented version looks more attractive.