A feeder will roughly double the number of birds you see in a small garden, and at least triple the number of species. The trick is matching seed type to the birds you want — and to the feeder design — rather than buying generic mixes that mostly attract the species you already had too many of.
Seeds and who eats them
Sunflower hearts (the kernels with the shells removed) are the closest thing to a universal seed. Tits, finches, sparrows, robins and even larger birds all take them. They produce no shell mess on the ground. They cost more per kilo than mixed seed but waste almost nothing.
Niger seed (sometimes called nyjer) is tiny and black, and only goldfinches and a few related species really eat it. If you want goldfinches, this is what brings them — but you need a special feeder with small holes or the seed pours out.
Peanuts attract tits, woodpeckers, and nuthatches. They must be served in a wire mesh feeder so birds peck pieces off, never whole — whole peanuts can choke nestlings if a parent carries one home.
Suet (fat blocks, often with seeds embedded) is high-calorie and important in winter. Tits and woodpeckers love it. In summer it can melt and turn rancid, so use less or pause through the warm months.
What to skip
Cheap mixed seed is mostly wheat and red millet, which most small birds reject. The discarded seed accumulates under the feeder, attracts rats, and you end up with a yard full of pigeons eating the rejects. Pay more for a higher-quality mix or, simpler, just stick to sunflower hearts.
Feeder placement
Birds like cover nearby — a hedge or shrub two or three metres away gives them somewhere to retreat between trips. Too close to dense cover and cats become a problem; too far from any cover and shy species will not visit at all. Three metres from a bush is a reasonable rule of thumb.
Clean feeders matter more than people think. Wet seed grows mould; old seed transmits diseases between birds. Empty and brush feeders out every two weeks — more often in warm weather. If you cannot commit to that, run only one or two feeders rather than the full set.