in case you´re not sure about the knots for fly flishing, the general recommendation for tippet to leader is the double surgeons knot, and from tippet to fly the improved clinch knot. Plenty of drawings and instructions on the internet.
My local fly fishing shop dealer recommended me, for making the leader last longer, to tie a perfection knot (loop knot) at the end of it, then attach the tippet also with a perfection knot. Then, as you work your way up the tippet (due to lost flies or swichting them) you don´t eat up your leader. Once the tippet gets too short, you cut another piece and loop-connect to the leader once again.
Personally, when I snag with this system I alwasy break the tippet at the loop connection, while with the surgeons knot never. Makes me think the surgeon knot is better. In regards to the clinch knot, whenever I snag and break the tippet, the times I can recover my flies have always showed a neat clinch knot still tied to the fly, and the "break" a few inches up the tippet from the fly.