1) Fish often
Even a blind horse finds water sometimes. The more time you spend on the water the better the chances that you will stumble into the trout of a lifetime.
2) Fish where large trout are common
This is probably the most important tip of all. Do whatever you can to fish rivers that commonly produce massive trout. I have only caught two trout in the 10lb range: a 28” rainbow in Kamchatka and a 28” brown in New Zealand. In places like New Zealand, a few Alaskan rivers, Kamchatka, and Tierra del Fuego trophy trout in this league are regularly caught. In the lower 48 fish of this size aren’t as common but can be found. In the West I would rate Montana and Idaho at the top of the list and Pennsylvania in the East. Some tail waters in Arkansas, Wyoming and Colorado also produce monsters just below large dams.
3) Fish big nasties!
With the exception of some huge tail water trout that gorge on freshwater shrimp being out of a dam, most big fish eat big meals. If you spend every day on the water casting tiny dry flies you might have a lot of action but your chances of hooking a trout of a lifetime are slim to none. Monster trout eat sculpins, crayfish, big stoneflies and other trout. I fish a lot of really big streamers that I custom tie. Casting these 10” tandem hooked bunny fur contraptions will scar away most small dogs and make your arm fall off at the end of the day, but throw them often enough good things will happen! A more reasonable option is to dead drift one meaty fly like a zonker trailed by a smaller bead head nymph under a strike indicator. This keeps you in the game for big trout but also increases the odds of not going home skunked.
4) Fish on cloudy days and in the rain.
Large trout frequently eat under low light conditions. Since they are often eating meaty meals they often go long periods of time without feeding while digesting their last victim. Fishing at dawn or at dusk is a good bet. Cloud cover and especially a good rain will often trigger intense feeding in the middle of the day by big trout. When the skies turn dark I always grab for my streamer rod and try to hit a home run.
5) Night fish
This isn’t as popular when fishing in Montana as it is in some locations, but it does have its rewards. In my opinion fishing after dark is most effective on rivers that get too warm during the day. Sometimes the best water temperature window occurs in the middle of the night and this is when large predatory browns do their feeding. I don’t do much of this anymore...the thought of waking up to three kids between the ages under the age of five after 2 hours sleep is enough to scare me straight. When I was in college in Pennsylvania this was a fun option on some of the limestone streams in the center of the state. The key to night fishing is to pick out 2 or 3 big runs that hold large trout and work them methodically with large bulky streamers that push a lot of water.