When attaching leader to tippet you generally should never mix manufactures like Rio with Orvis ect.The compounds used in leader mat'l differ (generally speaking) one compound being a little harder than another thus weakening the knot when it's tightened.I'm not sure of all the mix matches or the compatable ones so I just make sure that I keep with the same manufactures.I personally use Rio tippet and leader and use a double surgeons knot for my connection and as others stated wet the knot before cinching also leaving a very small tag end so the knot does not pull through. As far a using flouro is concerned I usually only use it whn I'm fishing slow moving or still water when the fish have more time to inspect the fly and leader/tippet. Bono