I usually use a swivel to connect line to leader and im good with knots but for some reason i cant get a good line to line knot. its my fishing weakness i guess you can say. Any tips...know of a any good line to line knots. And does it make a difference

One of the best line to line knots is the Blood knot

Click on the Blood knot in this Orvis Link
http://www.orvis.com/orvis_assets/files/ index.html

Or try this link to Grog's Animated Knots
http://www.animatedknots.com/bloodknot/i