I still struggle sometimes, but the first rule is to get downstream of a big fish. Fighting the brute upstream is the way to go. In this case, hold the rod mostly vertical and then apply side pressure right before landing the fish to ease it in to the net. The fish that runs downstream is the real challenge. I have found that holding the rod at about 10 o'clock works for me, so the rod is pointed slightly downstream, but still has enough upwards force to stay the hook point.
The next concern is to keep a big bend in your rod, especially with the longer rods. You must keep maximum tension. Finally, Aaron taught me not to automatically get the fish on the reel, as I used to, this distracts you from the battle. Instead, use the reel only after the fish has itself pulled the slack from your hand. I hope this helps...I still lose plenty of nice ones-especially on the super fast takes when nymphing the fast water!
Remember that after a fish is hooked, its first instinct is to head for safe holding water. This is why they always head for the tail out. When they are swimming downstream, you actually have a good angle for keeping the point in, but eventually, they always turn upstream and then your same pressure will yank the hook from its mouth. Your goal is to pull the hook in to the fish's mouth. When they jump, go nuts and change directions (Housy rainbows), there is no good angle!
The same angles you use for fighting a fish, you use for hooking a fish. The downstream hook set is always best. If you are casting a rusty spinner upstream to a big brown in a tail out, simply lifting the rod accomplishes the same angle.