When placing traps, make sure they're against a wall, a couple of feet from any entrance points. Rats (and mice) prefer to run alongside a wall (you may be able to spot tell-tale greasy brush marks). Once you've set them, try to hold off checking unless you hear them go off - Rats have an incredible sense of smell and it can take a few hours for your scent to disappear, which will warn the rat that a human has been near. They'll eventually go back to using that route, hopefully via the trap.
Don't bother with live/non-lethal traps, the risk from contamination is very high and relocation doesn't help anyone! (Whilst naturally very clean animals, Rats carry all sorts of nasties!)
Peanut butter (smooth or crunchy), Nutella and bacon rind are very effective bait, but anything that forces the rat to engage the trap (rather than just snatch & run) is good...
Hope some of this helps, good luck!