“I'm trying to pack light.”
You're going on a trip to a foreign country for a few weeks. You're packing for the trip while your roommate helps you. You don't want to pack a lot of clothes because you want to be able to travel easily. You say this to your roommate.
I'm trying to pack light.
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You use "I'm trying to ___" to describe something that you want to do, but isn't easy.
I try not go visit Facebook too often.
This means that, in general, you don't go to Facebook.com – maybe because you think it's a waste of time. On the other hand:
I'm trying not to go on Facebook too much.
This sounds like you want to stop going to the site, but it's difficult for you to stop.
To "pack light" means to not pack a lot of things when you go on a trip.
I packed pretty light this time.