Figured since we've been getting some tutorials 'n stuff I'd throw down some of my own tips. I've been painting for over seven years, so I probably know what I'm talking about (I hope ). This is a general guide, so add your own input. I'll be updating it as well if I remember anything or learn anything new.
Priming: Lots of people actually don't know what primer is. Priing doesn't just mean painting your minis black or white. It's a special kind of paint that really clings to the mini and makes sure the paint you apply does the same. It's very gritty, and to reduce the chances of loosing the detail it's recomended you use spray primer (you don't need to get the nooks and cranies becaue you don't need to worry about these chipping).
The Undercoat: It's recomended that you paint the miniatures either black or white after you prime them. It's not necessary, but it can determine how the overcoats appear. Also, if you're speed painting Black lets you ignore the nooks and cranies, since they'll be left black. Also, Black primers are often rather grey, so it can look ugly if you paint right on top of them. There are also grey primers though.
Basecoats: When you paint a surface, you start by painting it a slightly darker shade then it will end up. This is called a basecoat, and will give the lighter coats something to adhere to. Paint is just slightly transluscent, so painting a surface grey before painting it white can save you a lot of trouble and layering. Some choose to basecoat the entire miniature before moving on, while people like me prefer to do one surface at a time.
Highlights: Since miniatures are smaller than life, their shadows are less exagerated. It is thus important to manually make the higher surfaces lighter and the deaper darker. After you've basecoated a surface, either lighten the color by using white, off white, or yellow, or simply use a lighter shade of the color. Paint the raised surfaces and those surfaces that get hit by the light the most with the lighter color. Water down the paints to acheive a smooth application and to allow you to layer on successive highlights. Keep highlighting until you're happy with the surface. Make sure to admire it from afar as well, what looks good up close may not even be visible on the gaming table.
Shading: this is rarely necessary, but its essentially the opposite of highlighting. Paint the recesses with a darker shade of the basecoat. Keep the paint very wet for this, as it's help it flow into the recesses.
Watering Down Paint: most paint lines supply paint that is thicker than necessary. In this case it's good to use water, a thining agent, or even saliva to water down paint. this allows for a smoother transition when highlighting and better control. It's a bit tricky at first, but it makes things much easier in the long run. Try and get the paint about the consistency of milk.
Blending: This is a fancy work for really smooth highlighting or transitioning from one color to the next. Just use lots of highlights that have been watered down heavily. Another technique is to paint each of the extremes of the surface their prespective colors and then blend the middle by mixing the two. This allows for you to better control the highest highlight of the color. Both work just fine though.
Drybrushing: This is a very easy way to highlight things but the results are a bit messy. Take a large brush and coat it with paint. Wipe what you can off on the edge of the paint pot or pallette and then wipe off more on a paper towel. Then quickly brush over the desired surface of the model. The paint will adhere to the raised surfaces and never touch the recesses. Make sure not to water the paint down though, or it may run a bit or simply not come off the brush.
Sorry I have no pictures, I need a camera . More techniques and tutorials to follow though.
Edit: Changed the title, slapping my name on something and then asking others to contribute is no good.