q) how do i avoid this? what am i doing wrong? or is it just down to
learning how to use my trowel correctly? does the trowel need a
sharper edge on it? if so.. square? or beveled?

I spent months (or it seemed like months) plastering a 6 x 3ft section of
wall. I eventually got it relatively smooth, but not a patch on what a pro
plasterer could have done in 5 mins for about £40.

I hate to sound defeatist ('cause I'll give most stuff a bash!) but
plastering really is a black art and can drive relatively sane people to the
brink. If you really do have excessive time on your hands I would practice
on a 'spare' bit of wall first - plaster it, polish it, scrape it off before
it sets, repeat 5-10 times. But honestly, don't despair if it still looks
crap. Pro plasterers have in-built spirit levels and gyros to keep
everything flat, IMHO. :-)

Unless it's just bits of patching I always pay a plasterer now.

Andy