Peter t.
The best advice I can offer, is to get yourself in a position where your enthusiasm isn't going to be squelched by failure due to lack of knowledge.
Gathering from the wild, seedlings and such.. seems so straightforward; but it needs knowledge.
Practically, get your hands on two-dozen Larch seedlings about 2 feet tall. Garden centre material.
Plant half of 'em in the garden and leave them alone.
The other half, are your practise pieces and with these you can learn the rudiments of pruning, feeding , potting , training and design.
Meanwhiles, read up all that you can...
You will be very lucky not to lose some of the practise pieces, but, it aint the end of the world.
By the time you've really got your teeth into the techniques, you will have a dozen sturdy Larch to really go to work on.
Join your local club and get on a www bonsai forum.
regards
Ceeg