Great, you've just gone and bought a variable speed router. The salesperson probably talked up the advantages of variable speed, but I'll bet you've totally forgotten by the time you get home? Never fear, the main advantage of variable speed is the ability to slow down larger diameter cutters. The gereral rule of thumb is as follows:

Up to 25mm diameter: 24 000 rpm
Up to 50mm diameter: 18 000 rpm
Up to 63mm diameter: 16 000 rpm
Up to 90mm diameter: 12 000 rpm

To judge if your rate of feed or travel is correct, bear these tips in mind: If the edge of the timber is burnt, either your bit is blunt or the feed speed is too slow. If the bit 'chatters' your feed rate is too fast and not allowing sawdust to be cleared from the cut.

Some other worthy tips:

1. Always keep router bits sharp! If you destroy your router bit or workpiece because the router bit is blunt, the only one to blame will be yourself.
2. Never push a router bit all the way down in the router collet, you will never get it out again. As long as 3/4 of the shank is in the collet, you should be safe.
3. Do not take big cuts all at once, be sensible and take progressively deeper cuts for safety and a better finish.
4. Avoid using too many big cutters on 1/4" shanks as they are more prone to breakage and not covered by warranty. If you find that many of the cutters you use are large, don't be a tightwad, buy a bigger 1/2" router!
5. Listen to your router. If it is struggling, adjust your feed rate, sharpen your router bit or take less material off with your passes.