The simplest way I have, when arranging songs, is to ensure auto crossfades are switched on, select all the audio clips in question, then slip-edit the start points 'left' so that they crossfade with the clip before them. This only works well if you were recording before the start of the clip - a hard punch-in won't work there.
As for making loops loop seamlessly... this is something the Loop Construction window should do, by giving you fine control over loop points and crossfade options, before being able to render it down... but instead, the Loop Construction view seems to do a bunch of other things but not actual Loop Construction. Odd.