Winter, probably the least fished time of the year. Freezing temperatures, iced guides and tough fishing, combine to create the unholy trinity of why many of us would rather ski, tie flies, or binge watch romantic comedies during the colder months. Ice Ice baby
Winter fishing can be a lot like seeing your extended family during the holidays. Uncomfortable and awkward but if you can embrace the suck, you can grab yourself a slice of grandmas awesome apple pie (with ice cream) at the end, making the gathering almost worth it. Plus you know Uncle Gary is going to have 8 too many bud heavies and create a spectacle that rivals any MTV reality show.
Winter fishing is a lot like the above, minus Uncle Gary. If you can get through the bad you can be rewarded with some trout and especially some solitude that is often too hard to find during the warmer months. For me, winter is the start of my personal fishing season, while not ideal, I try to make some lemonade (not mikes hard) out of the lemons. Listed below are some things that have helped me have more fun in the winter. Hopefully they will help you!
Don't be a Martyr
For some of us this is easier than others. If you have flexibility in planning your day on the river, try to pick a day thats on a warming trend. Looking at the night time lows and daily highs can help narrow down the day to fish. Try to choose a day with the highest of each. If you're already committed to a day that looks miserable, hopefully the following steps can help you squeeze some lemonade out of winters lemons.
Choosing Water, Patterning Where the Trout Are
Choosing the right water type can be vital in winter fishing success. This is critical on a freestone river where flows and river temperatures can change drastically throughout the day. A tail water in the winter is usually the safest bet. During the colder months trout generally can be found in the deep slower runs and pools. In my winter experience, depth is the most important. For here in New Mexico, that means I'm usually looking for water that is waist deep or greater regardless of surface speed. I tend to find that if the trout are on the feed in the slower stuff, I can usually pick up a few in the shallower stuff at the head and tail out of the run. I also tend to let the water warm up before I go. Rarely will I fish a freestone before 10am, it's also important to note that water will be the warmest at the end of the day. If you're going to see a baetis hatch and have a shot at some dry fly fishing, it usually coincides with the warmest water temps. Remember there are no hard and fast rules in fishing just generalities. Don't be afraid to experiment.
Rigging for Success
I primarily fish a Euro rig in the winter time but will also fish suspension rigs as well. A European nymphing system is effective but the big disadvantage is your radius of presentation. I tend to wade aggressively to compensate for my lack of distance, but with ever step I take i'm flirting with the potential to fall. Dunking in the winter is not only the opposite of fun but can potentially be deadly because of onset of hypothermia. If you have to think twice about wadding into a good spot, don't. You have too much to risk. In larger rivers with bigger flows I favor a suspension rig to limit my wading.
With the colder water temperatures trout generally tend to hangout in the lower third of the water column. Down low they don't have to expend as much energy for their slower metabolic rate. Keeping this in mind affects my rigging greatly.
On a Euro rig I'll fish my heavier fly on the dropper (top fly) and my lighter fly on the point (terminal end). Fishing the heavier fly on the dropper will keep both flies closer together in the same band of the water column. From the tippet ring I'll run a length of tippet at depth or slightly shorter than depth where my dropper will be, before splicing in another two feet of tippet for the point fly.
Weight of flies and water speed will dictate my tippet and fly selection. If you're unsure 5x is a good place to start. In my local freestone I tend to favor something simple (Rainbow Czech) to tie because I tend to loose a lot of flies nymphing deep in the winter. I"m not risking a dunking over a fly. I'll usually run an egg pattern as my point fly. After the brown trout spawn in the fall, many eggs will wash down through the winter months and provide easy protein packed meals for trout, including browns themselves. For picky tail water fish I'll rig the same way. Usually in the winter tail waters will have a lower flow so I'll still put my heavier fly on the dropper but it will usually be a perdigon with a 2.8 - 2.0 tungsten bead with an unweighted midge on the point.
My indicator set up is very similar to the one I described above. I'll run 1.5x water depth from my indicator to my first ( heavier fly) and tie two feet of tippet off to my lighter fly.
TLDR
In short, try to pick a warm day, fish deep and slow, and most importantly have fun!