There's not a set, single tension that works for all bikes. It's just trial and error.
You need to pull it pretty tight before clamping it to the derailleur. Probably as tight as you can. Usually I find that's still not tight enough, so I screw the barrel adjuster down all the way before putting the cable in and then open it up until the tension is correct.
Assuming that you do in fact have everything else set up correctly: if the derailleur is rubbing on the outside of the chain, you need a little more tension. If it's rubbing on the inside, you need a little less.
Also, if you've swapped any parts out, you may be having some compatibility issues. Derailleurs have minimum and maximum chainring sizes. If you're just a smidge over or under those sizes, you're almost sure to get some rubbing.
If you can find it, it wouldn't be a bad idea to look at the owner's manual for your particular derailleur.