I am not sure what prog you are using (suspect CC3) or if this is compatible, but do a search for Ramah's "Tree Thing". It is a nice little script which works with tree images to make forests. Works quite well IMHO. As for any tips, it would really depend on the prog....not that I am much of an expert on any of them either - there are much better people to ask around here- but try looking at the stroke frequency...or whatever controls the density of the brush/fill. For links, look through the Finished Maps or Cartographers Choice sections and you should find some that are using a simular style.