If you're after getting tension into the line, I'd normally use a Truckers Hitch. This uses a loop to create a pulley - and there are various ways to make the loop. I tend to prefer either an Alpine Butterfly (as it doesn't get hard to undo after tensioning) or the loop of a slippery overhand knot (as it can be undone easily).
If you have issues losing tension when tying off the truckers hitch, you can opt to use a "wrap and re-wrap" method. Not sure that's the right name. Basically you pull the rope round the tree, round the taut line and back round the tree (back the way it came).
You can repeat this, going back and forth round the tree, any number of times. Then you tie off the loose end to the taut line.
This wrap and re-wrap method can be seen demonstrated about 90 seconds into this video: https://youtu.be/zdn1MlOUFuA?t=90 - albeit without doing a truckers hitch first.