The best 2 ways to prevent weeds is by mowing regularly, and choose a lawn like Buffalo or Zoysia that naturally competes well with weeds. As for killing and keeping weeds out of your lawn, read on...
Broard leaf weeds have broad generally flat leaves and can be sprayed out of your lawn with chemicals like Bromoximal MCPA, often sold under the brand Bindii Killer. If you've got Buffalo grass, be certain you use one compatible with Buffalo.
Broad leaf weeds include clover, Bindii, thistle, Capeweed, Creeping Oxalis, Cat's Ear and more. You can utilize either the chemicals diluted into your spray pack or unit, which is generally the best way. Spray the lawn and naturally the weeds will die, and the lawn will be unharmed.
Other options include utilizing a clip on hose herbicide such as Yates, which you'll find are very simple to use, but on some harder to kill weeds like Clover are not as effective as the mixture you would make up in a spray unit, but particularly for other weeds they work nicely.
Weed and feed products 'seem' good, but horticulturist tend not to recommend spraying a weed chemical and fertilising at the same time. It is advisable to keep these processes separate. Some clover weeds tend to be particularly stubborn, and you may need to use a stronger chemical, but unfortunately these aren't available to the general public, so you may need to hire a specialist, or just simply kill the areas dead with round up, and then replant, or try stronger frequent applications of the broad leaf chemical available to you.
Keep an eye out over winter for Bindii to develop. It may take a number of applications in order to get them all, as they germinate at different times over winter. Remember, stop weeds before they seed, and you can expect to stop the next generation.
If you've got Couch or Zoysia, you can use a specialist to take many grass weeds out of your lawn with commercial chemicals. You may also spot grass weeds out by yourself utilizing Round up or other mechanical methods. This works for all lawn types, including Buffalo, and Kikuyu, in addition to Couch and Zoysia.
The most simple method to remove them is to chip them before they seed. Use a knife, a pick, or a specialised weeding fork, which definitely works the best. However if you must, another method is to use a wick wiper filled with round up. Simply wipe the herbicide on the weed, and it'll die.
You might need to repeat this in a couple of weeks. Make certain you do not get any on your lawn. Sometimes you will have Kikuyu located within Buffalo lawn. To kill it, I'll get comfy, and paint the round up on, making sure you wear a rubber glove. Alternatively you might want to use a piece of Cardboard below the Kikuyu and above the lawn, and paint the round up on your Kikuyu.
If you have a Couch or Zoysia lawn, specialists can take out Kikuyu with commercial chemicals which are not generally available for home sale, however DSMA or MCPA is at the moment available in some home formulations such as Paspalum killer, and maybe used to take out stuborn grass weeds such as Kikuyu and Paspalum in Zoysia and Couch.
See to it that you read the label carefully if you choose to do it yourself, as the label might vary from product to product. Some claim these chemicals will take out nut grass too, but generally Sempra would be a better option. Having Nut grass, there are specialist nut grass killers, however they are usually so expensive for a small quantity it is better value to hire a specialist commercial weed killing service, although recently Sempra has appeared on some websites for as low as $69.95 for 25grms.
Non chemical weed control methods.
Mow regularly, and utilize Buffalo or Zoysia lawns. Apart from that you can chip or hand weed. Steam or hot water may also be utilized to kill weeds. The steam or hot water if used correctly will kill Broadleaf weeds without harming turf grass, however I suggest experimenting on small areas first to find out for yourself how best to do it.
It might also be dangerous, so maybe Round Up could be safer. These days you can buy small portable steamers. Plug these into an extension cord, and steam the weed to death. For the ones who really hate chemicals, your steamer can clean the bathroom, then kill the weeds.