What Svennn said. Not just in terms of mixing, but application as well. It's common for inexperienced sculptors to put a blob of putty on, then try to shape it to effectively reskin the figure, resulting in "clothing" that looks huge and marshmallowy. What you want to do is roll out a super-thin snake of putty only around 1.5 mm thick, then cut tiny bits off that to build areas/details selectively. If you need say, to cover a bare arm in a sleeve, don't just wrap the arm in a blob of putty and try to push it to shape. Use slivers of putty to build the draping under the arm, than the cuff, then any individual folds/creases on the top. Remember that even with thick, loose clothing there are a lot of points on the figure where the scale thickness between the cloth surface and the anatomy underneath is paper-thin or less, so the level of thickness you get by feathering individual folds and details out 'till the underlying metal shows or almost shows between is actually correct.
Also: buy a box of round toothpicks. If you find you need/want a particular tool shape, but don't have it, you can just whittle a toothpick to shape in moments, and it'll work just as well as a fancy expensive tool (it just won't last forever like a "proper" tool). In fact unsealed wood actually has one nifty advantage: it soaks up liquid, so it can be loaded with a lubricating/smoothing solvent like a felt-tip pen.
You can similarly make custom "clay shaper"-like rubber tools (again: works well, just doesn't last like the real thing) by carving bits of fine-grain pencil eraser, like the ubiquitous
Staedler "Mars Plastic" eraser. Pink school erasers are grainy and crumbly, so don't bother with those.