I'm doing the same thing with my paladin as he is level 38 right now.
There isn't much to it at lower levels, since paladins use a fixed rotation 696969 ans so on. They are a bit different than other tanks that use a prority based rotation.
You don't get all of your main tanking abilities until level 75 so just use whatever you have at your disposal at the moment, mainly consecration on every pull and using your Hand spells for alot more utility. You should have no trouble at all tanking with the paladin.
Just a few things to note for, at lower levels mana regen is awful for paladins but threat isn't an issue. So 1 consecration is enough for every pull while keeping up holy shield and Blessing of sanctuary, while just using Lay on hands if you get in trouble and hand of prot on the healer if anything is attacking him. You will learn alot while leveling.