Regular mowing and scarifying helps. I rake over parts of my lawn before mowing to lift the creeping type of weed, I also spot treat with weed killer if I can not remove it by hand. Dont forget that weeds may be killed off through the use of weedkillers or hand removing, but new ones will appear so its an on going job. The more you look after your lawn the less the weeds will flourish - aim to thicken the grass through regular mowing every 3-4 days in the growing season which will also weaken the weeds.