Most modern cars use MacPherson struts in their front suspension (and some in the rear as well) for their simplicity and predictable handling. There are several moving parts to the front strut suspension and, as it's subjected to a relatively hard life, failures do occur.
The bearings in the top mount can wear – leading to notchy steering, unusual noises, and wayward handling. Coil springs can crack, causing knocking noises and odd handling. The strut itself can leak, or decrease in performance over time. Balljoints and bushings in particular can fail and require replacement, and pretty much any component that moves in some way will wear out eventually.
In some cases these issues can be addressed with the strut 'in situ' but for other repairs the strut must come out, and come apart.
To replace the strut insert/damper, top mount, or coil spring you will need to use a spring compressor. These are straightforward to use, but care must be taken as the springs are under a great deal of pressure, and failure of the compressor can have catastrophic consequences!
Depending on the arrangement on your car, there are a variety of tools you may need, but in general you can remove most front struts with a basic tool kit. Be aware that most of the bolts will be VERY tight, so even a 3/8 inch drive ratchet set may not be enough for the task.
A ball joint splitter may also be needed to pry the control arm and tie rod end away from the bottom of the hub. Some setups feature Torx bolts too, so check to see if your car has them, and what size bits you’ll need, before starting.
If you do need to take the strut, spring, and top mount apart, then you will need a spring compressor. These come in the hand-held variety, which you hook over the spring and 'wind in' to compress the spring, or as a stand alone unit which the whole strut fits into. Whichever you opt for take care, as there is a LOT of potential energy stored in a compressed coil!
There's not a great deal you can do to prolong the life of your front struts and associated components. They will gradually decrease in performance over time regardless of what you do – but giving the suspension a regular visual inspection can catch potential problems before they become more serious.
Always investigate unwanted knocking, banging, creaking or scraping sounds that occur as you drive.
Ignoring one issue could lead to others. Similarly if you notice a strut leaking, replace it and its mate (always replace in pairs across the axle).
It's also worth mentioning that 'overworking' the suspension can shorten its life – so avoid thundering over speed bumps, or speeding along unpaved, or badly surfaced roads!
Coil springs and shock absorbers should give many years of trouble free service, with cars often running on their original coils for decades. Often the only time these components are replaced is when they fail. The dampers inside the struts are typically good for more than 50k miles, and it is sometimes twice that before they leak or get the floaty feel that leads to them being replaced.
But it's worth remembering that old/worn suspension can affect not just the handling, but also your braking distances. So if your car is getting on in years and miles consider refreshing the struts with new dampers.
Bushings and top mounts should also be replaced whenever deterioration is identified, and always when replacing the struts.
As long as you have a decent tool kit replacing struts isn't an expensive undertaking, with an average replacement damper costing around $50. But, it's not a particularly easy task, as many of the parts are likely to be very stubborn. It will cost you more money to buy a "loaded" strut with coil spring and top mount included, but it will save you a hassle.
Removing ball joints, can be tricky, plus the strut is likely to need a fair bit of 'persuasion' to remove if from the hub/knuckle.
It's one of those DIY tasks where you're better off knowing exactly what's involved before attempting it, and one where an experienced assistant is invaluable. When everything is back in place, you will also most likely need a wheel alignment to reset the proper camber.