First figure out what NOT to trim
Basically, what is the "meat" of your life? People only NEED a few things, like food and water, air, some form of shelter to keep them from harm… but beyond that, what makes your life undeniably yours? Relationships, home, job, family… This is the area you DON'T need to trim; because it defines who you are.

Then…

Trim the meaningless
This is the obvious fat. Stuff that means nothing to you, whether it's physical clutter or some activity that you do… it just brings no sense of fulfillment to your life. Simply put - get rid of it! If it's "junk" then literally donate it to charity. If its some sort of activity that you don't need or want to do, let someone do it.

Trim the "cling-ons"
These are the things that are around because THEY feel it's important. Now this is not advice on being selfish, but it is a lesson in how to be self-caring. Carefully evaluate why something is hanging on to your life. If it's not mutually beneficial, then perhaps it's time to change it.

Trim the time wasters
There are some things that are meaningful to you, but just take more than they give. It could be a long-winded conversation with a loved one, or some other activity that just always takes longer than it should. For this, you just have to learn short cuts and ways to politely know when to end things. Once the value is gone from the time spent, it's time to spend that time someplace else.

Add more "meat"
Fortunately time is finite in every day; so you have to choose wisely what to do with it. If you just trim the "fat" you'll be left with pockets that can just get filled up with different "fat." By adding more meaningful stuff to those moments, you won't have any more time to waste.