Follow the instructions on the label. If something says hand wash, hand wash! Don't put it in the washing machine. You can't just chuck everything in together, some things need washing at 40, others at 30, so make sure you look and seperate these. If you wash them at the wrong temperatures you risk the material deforming and the colours running or fading. Make sure you wash wools on a wool wash, otherwise they will bobble / shrink / not stretch.
If you have tshirts etc with prints or detail such as stuck on rhinestones then wash them inside out.
Once you've seperated these out then you need to wash similar colours together. Don't put your whites and light colours in with bold and dark ones, otherwise your white clothes will go grey and your light colours will look horrible.
If you have something new that's a particularly bright colour (reds in particular) wash it on it's own the first time round so that the colour that hasn't fixed yet can run and you don't get stains when you put it in with the rest of your laundry.
It is also a good idea to wash all your blue denim (jeans!) together as a wash because the indigo dye in denim often comes out. Once you've had the jeans a while and they've been through the wash a few times then you can put them in with the darks. Make sure you always wash them inside out!
In the case of structured clothing (ie collared shirts) make sure you reform them immediately after you take them out of the machine and hang them up (not on a clothes horse! A coathanger on a curtain rail is fine

) this will save you a lot of ironing and will also help the garment to keep it's shape.
And if you are ever in doubt about something, hand wash it!
Remember that the instruction labels are there for a reason. If you follow them and take care of your clothes properly then they will last forever, even cheap Primark stuff!
