The biggest and best piece of advice I can give you is to invest in a kitchen scale, and to weigh the ingredients in the recipes you already use. Most serious bread-makers think of their breads in terms of a "formula," or each ingredient's percentage by weight. Typically this is expressed as a percentage of the flour, ie the flour is 100% and everything else works from that.
It's typically your hydration -- the amount of liquid as a percentage of your flour -- that determines the dough's stiffness, though other ingredients always play a role. I find bread machines don't play very well with wet or "slack" doughs, so I haven't really pushed the envelope in that direction. I would suggest your hydration for a successful bread machine loaf probably falls in the 60s, give or take, and that's probably where your existing recipes will fall once you weigh them and do the math.
Personally I use mine just for mixing (which every machine does pretty well) and bake conventionally in my oven. If I'm experimenting with something other than a fairly conventional loaf, I usually mix by hand or make a small batch in my KitchenAid (small because it's useless for anything larger).
Edited to add -- the whole point of this pre-caffeine ramble -- that once you know the ratios of your existing recipes, which are proven to work in your machine, you can improvise all you want by observing the same ratios and then tweaking the ingredients from that starting point.
