How to keep an oven tray clean? Help me!

[DreamyCyanFinch]

Can anyone give me advise on how to keep my oven tray clean.Should you clean it as soon as it's cooled down.What do you use to stop it getting black, and really greasy.
Sorry if this is really obvious, but I had an old one that got really horrible and I tried everything even using a dishwasher tablet, I couldn't get it properly clean.

Cover it with foil when you are cooking. That should help.

I just stick them in the dishwasher

Thank you , I usually use bakimg paper, but foil is better?
Okay I will see if it fit in my dishwasher, not sure as mine is a bit small but I'll look.