As well as keeping feeders topped up, the charity suggests autumn is a good time to put in bird-friendly plants.
Bushes can attract insects in spring and summer and produce berries in winter.
Blackbirds, song thrushes and waxwings are among the birds which come closer to gardens in search of winter food.
BBC Springwatch presenter and RSPB vice president Chris Packham said he finds feeding birds in winter a rewarding experience.
"It makes me feel good about myself, knowing I could be helping a bird survive the winter and go on to raise chicks next year. It's a nice feeling," he said.
"You can see the good you're doing the way the birds just pile into your garden looking for food."
What kind of bird food should you be putting on your bird table this winter?
Here are some suggestions from the RSPB:
- Nyger seed will help goldfinches
- Mixed seed is good for house sparrows
- Fruit will be popular with blackbirds
- Put out kitchen scraps like grated cheese for wrens
- Unsalted bacon (cooked or uncooked) will be enjoyed by blue tits
- House - sparrows rely on a healthy supply of insects to raise their young.
They have declined by more than 60% in the past 25 years, according to the RSPB.
The charity says if you plant nectar-rich flowers and shrubs now, you will be helping sparrows in the spring.
What kind of bird-friendly plants could you put in your garden?
- Hawthorn, ivy and honeysuckle will provide berries in winter for adult birds, and insects for young birds in spring.
- Goat willow and dog rose will also attract insects.
- Once they are mature rowan, holly and apple trees are a great source of food for birds like blackbirds and thrushes, while robins and starlings will feast on the insects that thrive on them.