what is the best method to coat biscuits in chocolate
Whenever I work with dipping chocolate, I put a sheet of baking paper on my working table and place a cooling rack over it. 

This has two advantages:  


Excess chocolate can dripp off easily, without pooling that can happen when when the cookies are placed directly on the paper. 
The paper below makes cleanup very easy because the chocolate can be peeled off and reused if it contains no crumbs. (Admittedly I rarely reuse it because my children generously take care of the leftovers...)


Liquid ("tempered") chocolate will be too runny to be spread with a knife. If you let it cool down to a spreadable state, you will get a very uneven and streaky surface. If you have only a small amount of chocolate available, you can use a pastry brush (which may also leave streaks, but less), but usually dipping is the way to go: Melt enough chocolate that the height in your bowl is more than half of your cookies diameter. (Kind of obvious, but noted just for the sake of completeness.) Dip the cookie in, let excess chocolate drip back into your bowl, then lay it flat on the rack to cool. No need to prop them up or so. Leftover chocolate can be stored for your next batch or makes a good excuse for serving hot chocolate.

Some geometry: 
Note that dipping half a cookie will also coat the underside because you hold the cookie's edge perpendicular to the chocolate. If you dip only the top, you won't get a straight line, but always a crescent-shaped undipped part. If, for some reason, you want a straight line and a chocolate-free bottom, you need the pastry brush again.