..you're going to pull his forelock?
I wouldn't do that..
I've never seen anyone pull a forelock. It's a lot more sensitive there. I don't think he would appreciate that so much!
A handy tip is to pick up some thinning shears, like these:
And use those to cut the mane (just a little bit longer than the desired length) before you pull it. Doing this gives you less hair to pull so that it's less work and leaves his mane thicker. It's a little bit hard to get through the mane with these, and don't expect it to look perfect after this step (that's what the pulling will be for), but it gives a much better result than if you were to just go straight to pulling or cut it with scissors (because the lines would be too straight and it would be harder to pick the right ones to pull, etc)
Now onto pulling. This video really helped me learn to pull a mane.
I prefer to do everything by hand so that I have more feel for it and don't hurt the horse (because generally if it hurts you to pull it out it probably hurts him too so you can learn from that and take a smaller amount instead) but you can also pick up a pulling come and do it as the above poster described or as shown in the video. However works best for you and your horse is the best way to go with that.
If your horse's mane has uneven thickness like mine, you will want to pull more in some areas than others. For instance, if it's thick around the middle and thinner towards the withers, you will want to pull a lot from the middle and avoid pulling it much at all near the withers. Instead of pulling there, you can shorten that hair using average scissors, cutting STRAIGHT UP into the hair, holding the scissors totally vertically and cutting just a bit off of the tips at a time. Always avoid cutting horizontally with scissors (except for the thinning shears.)
To check your work, you should be able to squat down at his side next to his shoulder, to the eye level of the tips of his hair, so that you see it all lined up. You should see a straight line all the way up the mane. It also helps to take a few steps back and observe your work from a distance, to be sure that you have the right angle and nothing is uneven.