Are we talking the chrome strip that goes along the bottom of the glass or the rubber seals that the doors close against?
If it's the chrome one, the main thing is don't bend it. I removed one of mine to treat some rust and bent it a little, the combination of a rusty door skin and a bent strip has meant it'll never fit on properly again.
If both the door skin and the strip are in good condition, it should just 'pop' into place and the clips will hold it to the door skin.
Let me know if i'm barking up the wrong tree.
I'm back home to be reunited with my truck on friday, so if you want me to check anything then, just let me know.
See you soon