Rats are prey animals and they behave in certain ways to reduce their chances of being eaten. This page has advice on where to place your rat trap.
Rat droppings are small black to brown pellets about 7-10 mm long (slightly less than 1 cm to 1 cm). They’re a sure sign rats have been there, and a great place to put a trap.
Sometimes you might find trails, such as rat-sized tunnels in long grass or other low foliage, or footprints.
Not in open spaces
Rats don’t like open spaces (agoraphobia). Nor would you if you were trying to stay out of sight. Don’t bother putting traps out on the lawn or path.
Rats will stick close to walls, fences, hedges etc. when they move around. Not only do they provide cover, they help the rats navigate.
If you can’t reduce the food around, then you might entice them to try a new food source nearby. However, they may not try it.
If you can figure out where the rats live, then between the food and their nest would make sense too.
Under cover or foliage
In line with the open space advice, rats are likely to move under buildings, foliage, furniture, appliances etc.
Dry rather than damp areas are best. They’re probably better for your trap too.