I usually used a nail-less nail knot (similar to the nail knot, just without the need for a nail or tube) to connect the butt section of heavier ultra green (12lb) and used various lengths of 8-5 lb ultragreen or fluorocarbon depending on the conditions and necessities, for the leader and tippet. However, a common danger with the nail or nail-less nail knot, is the possibility of the plastic coating of the flyline stripping off on a larger fish or snag. To avoid such an unfortunate occurrence, I now use an albright knot to connect the mono to the flyline. It will never fail before the tippet breaks (as it should). The down side is there is more tag to clip (resulting in a shortening of the flyline) each time you need to retie it (which thankfully is not often).