Prevention is better than any cure
Proprietary stain repellants can protect suede against food and water marks. However these should only be used on clean items.
Protect the collar of a suede jacket from grease from your neck by wearing a scarf or high collar shirt.

General care
The best way to deal with suede is to care for it well. A suede garment will give you many years of wear if you look after it well.
Always clean suede before storing it for any length of time.
Suede can be brushed with a soft rubber or bristle brush, or a wire suede brush. Do not rub too hard and do it in a gentle circular motion.
Never use chemical fluid or spot remover on suede as the colour of the garment will run and you will actually get light rings around the stain.

Sad Suede
If your suede item is looking a little sad, flattened and in need of a 'pick me up', hold the material over a bowl of boiling water or a kettle spout. Allow the steam to get well into the nap, then brush it up with a soft bristle brush.

Stains and Marks
Most marks on suede can be brushed off with a stiff brush, a damp cloth or sponge. However grease and oil can be a real struggle to remove from suede. 

Grease Marks/Stains
Cover the mark with talcum powder and leave over night. The powder will absorb the grease. Brush clean in the morning.
Try making a thick paste of Fullers Earth and a little dry cleaning fluid and rub it into the stain. Leave for a few hours or overnight and brush it all away.
For grease marks round collars. You can buy special suede cleaning cloths that you can rub over marks such as these.

Water marks
Suede is very prone to getting water marks. Once the suede is dry you can remove water marks from suede  by brushing with a suede brush or stiff upholstery brush. You can also use a damp cloth or sponge. If ordinary brushing does not do the trick then try rubbing the area lightly with emery board, then steam over a boiling kettle.( Be careful with the steam )

Make up marks
Make up stains on suede can be removed by rubbing with a piece of stale bread.

Following these general rules should be a great guideline for looking after your item. See below for tips sent in by visitors

I bought an expensive very soft suede jacket in a beige colour but every time i wanted it cleaned to remove make-up etc it was going to cost me £40, so I put it in my washing machine on a 40 degree wash and it came out like a new jacket, when it was drying I kept reshaping it. It certainly saves on dry cleaning bills.