Small flies are required on some heavily pressured areas, especially tail waters.
The good thing about this situation is that large trout in these waters have to feed constantly to get eat the biomass that they require. So although the flies are small, the opportunities are great.
Use thin thread, and minimal wraps and simple patterns. Also, for small patterns, the hook eye is perceived by the fish as part of the body. The hook eye becomes larger compared to the hook shank as hooks get smaller. Therefore, a natural midge pupa that is the length of a 22 hook, would require a size 24 hook to match it because the fish incorporates the eye of the hook into the pattern.
Another strategy is to tie a double pattern. For example, when fishing trico spinners, tie two trico spinner on the same hook. Trico spinners falls are often heavy and during such spinner falls, the fish are used to taking several spinners on a single rise. The double spinner allows you to tie a two spinners on single larger and stronger hook to get more hook ups and also to put more pressure on the fish.
"A Double Trico Spinner pattern will help the angler by not just allowing the use of a bigger gapped hook, but also allow the angler to minimize the micro drag challenge as the fly will have a heavier placement in the meniscus of the water surface."
Fishing the Trico Hatch
Trico Double pattern
Here's a pattern from the trout Shop in Craig, Montana on the Missouri below Holter Dam. They get massive trico spinner falls. For big trout on tiny flies, they use a double pattern.