Hi matt, You can sow some grass seed now, it will start to germinate as soon as the weather is warm enough.
It really depends on how bare the patches are, if completely bare if may be worth digging it over and crumblig it finely or if it's just a bit sparse you could lightly fork it over.
Choose seed to suit your purpose ie shade, hard-wearing etc. sow thinly cover with some good top soil or compost and firm it down well then keep it watered in dry weather.
Some wire mesh wirt the edges turned down placed over the top should keep it from being disturbed. Good Luck Tbird+