The best practice is to launch it from the side of the wind window with a launchman however it takes a very good understanding of the aerodynamics and the shape of a foil kite not only from the part of the kiter but also from the launch man.
Here are the additional tricks and important points:
The launcher needs to keep the kite untill it is fully inflated and stable, however this requires a perfect lunch.
-the first thing to understand that, the more filled the kite the more it wants to fly to the edge of the wind window. So this mean that you start the launch in a bit deeper in the windwindow and the kiter should start walking downind as the kite tries to fly to the very edge of the wind window. You should play also with the bar to keep the kite vertical.
-the second very important point that launcher should hold the kite more at the trailing edge as he is pulling too much the leading edge part of the kite it will make a front collapse of the kite.
-the third very important thing for the launcher that he "has to put the filling kite on the right place". This means that he should imagine the open kite and he should let/put the kite on the right place. The launcher should only pull/keep the kite down and should not pull in any other direction, and this can be achived if he walks there where the kite want to go and be opened. A common mistake that the launcher is pulling too much the down part of the kite (what he is grabbing) in the direction of the kiter and he is causing a side collapse by breaking the form of kite. For the kiter it is very hard to see that is launcher is 1 meter closer to him and by this he is deforming and side collapsing your kite. So most cases the launcher should usally make a few steps away from the kiter to let the kite on its place. The reason for this that the kiter dont really see if the launcher is too close to him or not, and it would be also very hard for him to go backwards while the kite is tries to pull him downwind so therefore the launcher has to move and he has to walk a bit with the kite to the correct place.
If you have an unexperienced person trying to launch than probably sand works better. The reason is sand or sand bag works better than unexperienced launchers that sand or sand bag is pulling mainly downwards (by their weight) and by pulling downwards they open your kite (they even tend to move a bit with your kite to the correct place) however "stupid" launchers pulling the kite towards you like hell, so they deform it and side and front collapsing your kite and dont move their body to put the kite on the right place.
If you and your launcher fully understand the above than high wind side launcing will be a piece of cake