212 Slice the turn entry
In order to have a clean turn entry, it is necessary to have a clean exit from the previous turn. Another way to look at this is that if a turn is less than adequate, it makes more sense to look at the previous turn rather than focus on the turn that appears to be the problem. (If the toeside sucks, look to the heelside for resolution).
If the goal is to reduce the amount of skid at the turn entry, one should look at the causes of skid. The most obvious source of skid is one borne of habit, which is to say rotating the body in the direction of the turn. This happens by habit when a rider is on terrain that is too challenging for their level of skill development.
Rotational movements must originate and terminate on an anchor, which is to say, solid footing. The origin is not a problem, since the end of a turn is the place where a platform has somehow been developed. Between origin and termination, though, the board has gone flat, the opposite edge has been engaged, the direction of travel has changed, and possibly the consistency of the surface is now different. Momentum, both angular and linear has developed as well. Thus, skid.
The other cause of skid is inappropriate pressure distribution to the front of the board, and/or late rise in edge angle. Coming from a skiing background, too many people have the mistaken assumption that in order to make a turn, it is necessary to heavily weight the front of the ski and to stay there. While the front of the board needs to be weighted, if it is disproportionately weighted, the back of the board will not bend enough to follow the same path as the front. Begin a turn front to middle, and end a turn middle to back.
The angle of the board edge relative to the snow should rise progressively on approach to the fall-line. This ensures that the change in direction occurs gradually. If the edge angle remains low early, and is brought up suddenly, the snow will often give way under the load of a sudden change in direction, skid or chatter the tangible result.
The previous situations often arise out of an inability to move with agility out of the old turn and into the new turn. For instance, If the toe-side edge cannot be released because too much weight is on the rear foot, the turn can be terminated by rotating the torso toward the new turn using the locked edge as an anchor. If a turn is created by moving a large body part to tilt the board, that same part must be moved out of the turn in order to end the turn. This is often a dicey proposition. If the heel-side turn is initiated with too much weight on the front foot (common) the rider will sit to the inside of the turn to increase edge angle to counter the inevitable skid. The rider will lean the shoulders into the toeside turn, and as the board goes flat, kick the rear end of the board around until the toe edge begins to grip. If the heelside edge is engaged by pushing the hips diagonally forward, the edge will come up slowly until after the fall line, at which point it will either skid or chatter, depending on rider sensitivity and binding set-up.
So, look to turn completion situations in order to clean up turn initiation. Ideally, initial edge engagement will take place as a result of foot and knee movments. Particularly on steeper terrain, dexterity is required for accurate edge engagement, and to ensure that edge contact is not disrupted.
Another consideration here is whether or not the rider is up-unweighting at the turn connection, either from habit or misinformation. Due to the sidecuts on modern snowboards (anything built after, say, 1988?) there is no need to make the board light in order to initiate a turn. Doing so just inhibits the ability of the board to do the job it was designed to do. If a rider rises at the turn connection, they have to come down at some point later in the turn. This will often overload the board, which has already been reasonably decambered, and the edge may then lose its grip.