You'll want to learn these on a flat box first, preferably one you can get onto without needing to ollie. Make sure you can do 50-50s and boardslides comfortably before trying the front board. Trying out the motion on the snow is a good idea - you'll need to get used to the feeling of 'counter rotation' to do this trick well. Counter rotation is when your upper and lower body are rotated in different directions, like you can see in the picture on the right.
1) Approach the box straight on and keep your speed up! Keep your line nice and straight, focusing on the box you want to hit.
2) Even if you can ride straight on to the box, it will help your progression later on if you jump (off two feet) from your toe edge. Keep your eyes on the box.
3) As you jump you will need to rotate your lower body 90 degrees while keeping your upper body in line with the box. Most importantly, remember to keep your board totally flat on the box, like with 50-50s and boardslides.
4) If you want to come out forwards, you'll need to keep your upper body counter rotated. To make this easier, as you approach the box keep both your arms pointed backwards towards the tail of your board. As you jump to land in the frontside boardslide position, throw your arms forward towards the end of the rail. This movement will help you keep the board flat and pop out moving fowards at the end.
5) Keep even pressure on your board while sliding - most people fail on this trick as they have too much pressure on their toes while sliding, which generally leads to falling forwards onto the rail before the end.
6) Now you are approaching the end of the rail you will need to pop off either forwards or fakie. If you have your upper body counter rotated you should find it easy to pop out forwards. If you shoulders are in line with your board you will most likely pop out fakie.
7) Once you have mastered front board's on the flat box straight on, start popping onto the box from more of a sidewards angle (so your body is facing the box). This will help you progess to features where you will need to ollie on, such as street rails.