If the interest is in attracting a wide range of birds to your backyard, that general mix should attract finches, snowbirds (juncos), cardinals, blue jays, mourning doves and others to the feeder. It will also attract our more common house sparrow along with white-crowned and white throated sparrows. You will likely find that birds will sort through the seed available on the feeder, scattering unwanted seed around under the feeder. There are birds that are ground feeders that can benefit from this, yet it also is a great way to attract the overwintering and active small four-legged critters to the yard. Feeding birds using their favorite seed and several feeders will eliminate waste and save money in the long run. An example of feeding to attract a specific bird would be using thistle seed for several kinds of finches.
Either way, bird feeding should start sooner than later so the birds learn that food is always available to them in your yard. Birds will be finishing off available seeds and fruits as fall approaches. Feeding well into spring also is important because until nature begins to supply food again, those birds still count on your feeders. Migratory birds also have to eat along their journey, so you are helping them out as well. Make your decision about feeding early and keep the food flowing all winter. Feeding for just part of the winter means a higher mortality rate, as the birds became dependent on your feeders.
Buying enough seed to get you well into spring is one approach. Having the seed around that long means running the risk of introducing a common pantry pest, the Indian meal moth into the home. Purchasing small bags as you need may be a better option. Storing the seed in a tight-sealing container or keeping the seed in the unheated garage is a way to reduce the risk of finding the moths. Feeding into late spring as natural sources of food come available and not until the seed is gone means not having to store the seed which always guarantees no pantry pests. When you are done feeding, clear out the seed debris in the feeder before storing away for the summer.
Another aspect overlooked is a source of drinking water. On a sunny day, the snow melts, yet much of the winter open free water is not easily found. There are a number of commercially available bird baths that have built in heaters that will keep the water from freezing. Those with ponds that have circulating water all winter are providing water for more than birds too.