I fish lake travis alot and was wondering what is the trick to finding where to throw a cast net for shad and carp?and whats a good size of cast net to start learning to throw with?thanks for yalls help.

For the shad, windblown points, coves etc. Around boat ramps / docks can be good early in the mornings. As far as size, get the biggest radius you can throw. You may want to start with like a 5 footer. my .02

I have found the shad piled up in small coves at Travis (across the lake from you at Pace Bend is where I got all my shad in the little coves shad and perch) and like Fowlhooked said, the windblown side of the lake. I see you are from Lago...the marina has some great docks loaded with shad (the crappie house draws shad at night and you can cast off of one of the adjacent docks if you do not have a boat, and the docks are an ideal spot to stand to learn the net. If you have a boat search on your depthfinder for the clouds of color red blue and yellow, make sure you have enough rope on the net to get it down to them and let er rip.

I agree with fowlhooked a 5' net is a good starting net, dont short yourself on the weights on the net. Several good videos to watch before you go...heres one from a good guy named Eddie who is in Iraq right now. http://www.youtube.com/watch?v=iO7lAhaHQAg this is one of Eddies clean videos lol, he gets a little excited in his fishing videos. You tube name is EDDIE 978N. He shows you how to throw with about a 5' net.

I bought a 7'0 radius, I have been throwing a 5 & 6' for a long time, they have wrecked my shoulder, but I looked on the internet and found an easy way to throw and it dont hurt you, even when you have a big net with extra weight. Look this up!
http://www.calusa.com/howtothrow.cfm

Around boat ramps early and in the evening are good for shad. Also I stick to the places where I know my net will not get hung up. 5' net is a goodun.