Funny you should bring this up...I was just tweaking my tarp lines and thinking that it would be cool to get rid of any unnecessary hardware ala Ray Mears.
From my limited hammocking experience and mostly from my military experience as a communications lineman I found that I use these knots almost daily still. I am sure that others will have differing opinions, but these should get you by:
-Square Knot/Overhand (I don't really use hammocking but c'mon
-Marlin Spike Hitch
-Taut Line Hitch
As others have said, practice every chance you get. It is fun, relaxing and surprising useful knowledge. Just hangout on Saturday morning at Lowe's/HomeDepot in the lumber load dock and you will get good real fast.