Tricky things, meringues.
You need to get the egg whites well whipped so they hold their shape, but not overwhipped so they start to separate again. You need to make sure that the sugar is well-incorporated so the meringues don't weep caramel and water while they cook.

I mostly like my meringues to be a bit chewy in the middle, but if you're making Eton Mess those won't work and you'll want them hard and crispy all the way through. Some tips from around the web:

French Meringue
ingredient dessert veg
French meringues are made with cold sugar crystals rather than sugar syrup (Italian) or by heating (Swiss).
The ratio of sugar to egg determines the texture (hardness) of the finished meringues.
Firm meringue needs 4 tablespoons (about ¼ cup or 2 oz or 55g) sugar per egg white. I've also seen the weight of sugar described as twice the weight of egg white.
Soft meringue will start to set with 2 tablespoons of sugar per egg white. But no less.

Wipe around the bowl with half a lemon (if using).
Add in the egg whites, cream of tartar (if using) and whip the whites to nice soft peaks.
Add sugar.
Add flavourings if using.
Use an icing bag (or cut the corner off a small plastic bag) to pipe the meringues onto oven trays lined with greaseproof paper. Smaller shapes will dry out more effectively, and nests will probably work best.
Now either:
  • Cook at 105°C (Gas Mark ¼) for 1½ hours then leave in the (very low or off) oven with the door propped open to cool overnight.
  • Cook for 6 hours or overnight at 60°C (or as low as your oven will go).
To be honest I'm still working on getting the crunch right, but I can do chewy - no problem!

Crushed Meringue
ingredient dessert veg
A good coffee or chocolate flavoured topping for vanilla ice-cream.

Makes 2-3 cups

If using frozen egg whites, thaw them in the refrigerator.
Mix the sugar with the instant espresso or cocoa.
Preheat the oven to 250°F/120°C/Gas Mark ½. Line a jelly roll pan with aluminum foil sprayed with oil.
Beat the egg whites with a pinch of salt until they are very stiff, gradually adding the sugar and the vanilla.
Spread the batter evenly onto the aluminum foil and bake for 60 minutes, until dry to the touch. Remove the pan from the oven and leave the oven on. Transfer the meringue onto a large cutting board and peel off the aluminum foil. It's OK if it breaks into many pieces, as it will be crushed anyway.
Coarsely chop the meringue with a large knife and spread it out on the jelly roll pan. Bake for another 30 minutes, until the meringue has barely any moist spots left. Turn off the oven but leave the meringue in with the door closed, which will dry it further.
After the meringue is cooled completely, store in tin cans. It keeps for several weeks.
My meringue remained stubbornly chewy and I had to peel away the crunchy crust to crush up - but what I got was very tasty.