FOREHAND TRIMMING
There is a big difference between trimming on your forehand vs trimming on your backhand - with most people finding things a little easier riding forehand.
So let's start with the trimming on your forehand to get things started.
WHY IS TRIMMING FOREHAND EASIER?
Trimming on your forehand is made easier for a couple of reasons:

HOW TO TRIM ON YOUR FOREHAND
A lot of the work when it comes to trimming across a wave is all done in the set-up.
It comes from:
Execute these three things well, and setting your line to trim across the wave will be a breeze. However get any of the above wrong, it'll be almost impossible to achieve.
Lets break the whole process down in detail below:

QUICK TIP: SET YOUR LINE EARLY!
Alright, so trimming across a wave is made so much easier when you're able to set your line early, which involves popping up quickly, and getting your line set straight away.
This is important for a few reasons:
- Getting to your feet early is the safest way to ride down a green wave (if you're riding down a wave on your belly there's a high chance you'll nosedive).
- Setting your line early cuts off the steepness of the wave in the same way that a road goes around a mountain - rather than straight up - which helps to avoid nosediving.
- Setting your line early within the curve of the wave is much easier to do than trying to set your line in the flats.
WRAPPING IT UP
Just like painting a wall is 90% preparation: removing grease, filling holes, sanding, masking taping, laying dust-sheets, cutting in, etc.
And only the final 10% is where the glory happens, and you finally get to actually paint the wall itself.
The same holds true with trimming on a wave.
90% of the work is in the set-up.
Get all of that right, and you'll be crushing it.