I make sourdough pretty regularly (about once a week, sometimes more often, sometimes less often).
The trick is (for me, at least), is to have the dough as sticky and wet as possible, as this allows for good, air-bubbly, light but chewy sourdough. That's how I like it! I've made it in the past using more flour/less water, and while the dough is much easier to work with the end product is more dense and solid. I use a slight variation on the river cottage recipes - in that I can't be bothered measuring exactly and just mix it til it feels right. Make sure you use bakers/strong flour - I use either wholemeal or white, but I haven't used spelt before.
The other thing is to make sure that your oven is really nice and hot before you put it in - 250 degrees (celsius) is good. After about ten minutes, turn it down to 200 degrees, then cook until it's brown and sounds hollow. The timing is totally dependent on how wet the dough was, how big the loaves are, and how hot your oven is. If you want to get a nice crust, stick a pan of boiling water in the bottom of the oven to create lots of steam. Leave it in for the whole baking process, and limit the number of times you open the oven (as this will lose heat/steam).
Nice variations are:
- Fruit loaf - i throw in about a cup full of chopped up dried apricots and dried figs, as well as some walnuts (as many as you like). This does tend to make the bread a little bit heavier.
- Roast pumpkin and walnut or pepita loaf - roast some pumpkin with a little bit of olive oil - I like it when the edges are a little bit caramelised. If you're doing a roast (lamb, beef, whatever) with vegies, just make extra pumpkin. Whatever doesn't get eaten, put it in the bread! Also add either walnuts or pepitas for a nice balance. One of my friends requests this pumpkin sourdough for her birthday instead of a cake - it's pretty popular.
I add these extras normally just before the last prove, as if you add them sooner they get a bit broken up during the kneading process.
I would also recommend the River Cottage Bread Handbook - I've had a look at a few other recipes and books but this one just makes sense to me. They explain the whole process quite well - it's much better to have an understanding about how the yeast/gluten/heat/everything works, I find.
Oh, and have fun! Get sticky and gooey and then enjoy the results!