What is the best way to get rid of a rat?

I am a former pest control guy who dealt with many rats in my time, and I will only say this. They are difficult to deal with. But here is one method you can try. One thing to do, when you place the trap, is to make sure it is perpendicular to the wall as opposed to longways. I can draw a picture if that doesn't make sense. This is because rats travel usually along the walls and this way the trap will get them in either direction. When you first set the trap out, DO NOT BAIT IT AND DO NOT SET IT.. Rats are VERY aware of their environment and extremely suspect of new things that appear in it. If the trap is not set and not baited, they will become "familiar" with it and not be as concerned about it. After a few days to a week, when you know the rat is "comfortable" with the trap being there, bait it. But still DO NOT SET IT. Just bait it. Do this for a few days, allowing the rat to eat the bait. When you notice the rat is regularly eating the bait, you know he feels "safe." NOW set the baited trap. He's going to be quite comfortable knowing it is a safe place to eat some food and he'll go harder on the trigger. It doesn't mean you are guaranteed to snap him. But it's pretty likely you will. Hope that helps.

Shoot it?

Maybe try a different kind of trap? Because traps seem to be the overwhelming favorite if you can find the right kind.

I'll lock the closet in case the rat sneak in there.Then i'll learn to ignore them.They're too smart and fast to be killed. If you want to deal with them,you can ask for the expert,or you can narcotize them with the poison.Narcotic won't kill them,you can spend some time to find them and throw them out.

What are you using for bait? We've used peanut butter in the past as it sticks to the bait area and they can't just flick it away.

Looks like @porwest has helped you. Good luck.