when is it okay to check on river if you're first

and want to check raise. I am gettin burned on this. I also can't find the right amount to bet, i seem to get too greedy.

How are you getting burned exactly? Personally I prefer to just bet out on the river if I am first to act & have a good hand. A lot of players, ranging from very good to very bad, will check behind on the river unless their hand is a monster. Check-raising on the river is only a good plan against players you know are aggressive and will try to bully you out of the pot. ie. you are pretty certain they will bet, regardless of how strong their hand is.

If you do get the chance, I'd say check-raise an amount about 50% higher than your opponent's bet. He bets $2, you raise to $5. It's a callable bet that still shows strength. You'll get a lot of calls, a handful of folds, and sometimes an aggro player going over the top of you all in... in which case, you're on your own.

you have to have a feel for what you think is going to happen...

yesterday I cold called a river bet with the nut straight in between 2 others, KNOWING they would raise, which would allow me to push after they were totally pot committed. Sure enough, they did.