When doing bent over rows...

[chrisg]

should my chest be parallel to the floor when I'm bringing up the barbell to my stomach and also I don't know if I should keep my knees locked straight or slightly bent? Should I wear a back belt when doing them too?

[smaul]

This completely depends on which area of the back you are trying to hit.  personally I tend to do them fairly strict, use lighter weight and bent forward quite far with a good  squeeze at the top and goot stretch at the bottom.  Once in a while I am slightly more upright and do them heavier, this hits the muscles higher up between your shoulder blades more imo.  I tend to vary it all quite a bit.

[pumpster]

Try different angles-bend way over, not bent over much, etc. and decide what's comfortable on the lower back, that's all that matters. Same applies to legs, just use what's comfortable. Belts shouldn't be necessary, if you find the right angle there's minimal back strain.