Turning lawn into forest. When?

The steps have been described but I have been wondering about how long does this take? What can I do to help it along, i.e., speed things up? (I want food!) How can I be sure the proper mycorrhizae are in my soil for trees? What about a neglected lot that is gone to weeds? Would the process be quicker or slower there? What trees would be appropriate first trees to introduce?
Thanks!