Well I live in Phoenix, Arizona and I fish Bartlett lake, with no boat.
I moved from Ft. Lauderdale Florida and am used to offshore fishing so this freshwater buisness is new to me.

I have gone out fishing for flatheads probably 4 times now, and on my 4th time I was about to give up because I had never even had a bite. I had been using live bluegill on a Carolina Rig with 5/0 circle hooks. I have been fishing at night in about 3-10 feet of water in the coves, and have tried in about 25-50 feet of water at the dock. I went out with my cousin the other night and had one poll rigged with live bluegill and the rest with worms/anchovies for the channel catfish so we didnt get bored. I had lots of luck with channel at the lake before but none that were a good size. They were all pretty small. I had one pole riged with a crappie type rig I used to use at hilsburo in Florida in about 100 feet of water for kingfih. I had anchovie on the bottom hook and worm on the top hook.

After a few hits on the worms and one lost fish to a snag, about 12pm I got a huge hit from the poll with the modified crappie rig. I thought I had me a giant channel, but no as I wrestle in this 26 pound flathead on my 8 pound test I start to realize I just caught my very first flathead. Then I realize that there is a bluegill in his mouth. Turns out I accidentally caught a bluegill and he must have sat on my line and hooked a flathead when he went after the bluegill!

So that was it, I am hooked on flatheads. I want a monster now.
I need some tips. Should I try deeper water? What about sand beds, there are sand flatts at the lake I fish with a few points.... also I have been hooking the bluegill through the back dorsal fin. Should I try hooking them in themouth?

Also should I try a different rig? to get the bluegill off the bottom? I have to gotten a single bite on a carolina rig.
Also what is this about goldfish? Should I try goldfish? and were do I hook them?

Congrats on the Flathead 

That's a sweet story!  Sometimes it's better to be lucky than good.  It's pretty addicting after you get a nice one like that.  Good luck on your quest for a two hander, they're hard to come by but when you do get one it makes it all the more worth while.