Anyone else here into this? I've been feeding wild birds for a couple of years now and gotten a few DDFers hooked. I've also spoken to people recently who've wanted to get started now that they're stuck in quarantine.
The main thing I've found is to attract the biggest variety of birds you need to put out a variety of foods. That generic mixed bag of bird seed has its place, but most birds prefer certain types of food and have a preferred way of eating. The more you cater to their whims, the more birds you'd get.
At the moment my feeding station consists of 5 different feeders plus a bird bath, and I've observed 27 different species to date (
updated 2/13/21):
6 kinds of sparrows (chipping, house, tree, savannah, song, and white-throated)
3 kinds of finches (american goldfinch, house, and purple)
3 kinds of woodpeckers (downy, hairy, and red-bellied)
2 kinds of nuthatches (red-breasted and white-breasted)
American robin
Black-capped chickadee
Blue jay
Carolina wren
Common grackle
Dark-eyed junco
European starling
Gray catbird
Mourning dove
Northern red cardinal
Northern mockingbird
Pine warbler
Tufted titmouse
Here's my current setup:

(For the record, this is a composite photo of around 8 pictures from last Friday.)
1: Hopper feeder at top right, filled with seed mix. For sparrows, titmice, cardinals, and a little bit of everything else.
2: Perching tube feeder in the lower middle (with the yellow), filled with thistle seed. For goldfinches, house finches, chickadees.
3: Tray feeder just to the left of the tube, filled with safflower and whatever random thing I want to experiment with. For juncos, cardinal, wrens, bluejays, catbirds, doves, and more.
4: Suet cage (straight on top of the tray), filled with suet cakes. For woodpeckers, nuthatches, grackles, and starlings.
5: Oriole feeder all the way to the left, with orange halves and grape jelly. For orioles and warblers.
This entire thing is in a corner of my deck and positioned right outside my main kitchen window. A bit off the the side is the bird bath, which is clamped onto the railing:

I cannot recommend this enough. You don't have to go all-out - start with a basic hopper feeder and mixed seeds and you won't believe how many birds come. And yes, even in the city.
It is ridiculously entertaining to just sit and watch them. I've seen a cardinal couple bring their fledgling twins and show them how to crack open seeds, I've seen fights, courtship and everything in between. You'd hear a hawk calling and instantly all birds run for their lives, but they don't know that it's actually a bluejay doing a perfect imitation. A second later the bluejay soars out of the trees and has the place all to himself. You'd notice that the larger the woodpecker, the more scared he is of his shadow. I've even recognized individual birds who come back to my feeders season after season.
Most of all though, you'd just enjoy having that little slice of nature all to your own.
Any questions? Ask away!