Like many sculptors I am completely self-taught. In the same fashion as that with which I approach my painting efforts, when I sculpt I give greater importance to the overall feel of the piece rather than seeking technical perfection as an end in itself. That said I do strive to refine my rendition of details, after all: the devil is in the details... Although I would have got nowhere without the various, and sometimes excellent, tutorials that can be found in the meanders of the internet.
One of the biggest obstacles, when I started sculpting, was the fear of "getting it wrong", if there was one piece of advice I would give to anyone wanting to start miniature sculpting it would be: "don't be scared of getting it wrong, the putty won't press charges!". Also if you practice on oven curing putties like Fimo or Sculpey then you can keep working until you are happy with the result, or just squish it all up into a ball and start again.
The first tools I used were scavenged among the handful of things I'd accumulated. Later on, convinced by numerous tutorials that I needed a vast array of tools, I went out and spent quite a bit of money on clay shapers, dentist tools, tiny files and the list goes on... Finally, I ended up creating my own tools because for some reason, and despite all the tools I had deliberately bought, I couldn't quite get the results I wanted. Nowadays I use perhaps ten percent of all the tools I possess, and in that ten percent I do probably ninety percent of my work with one tool that I made and which probably cost me fifty pence and twenty minutes to make... Moral of the tale: the more you give a tool its chances, the more likely you are to save your money by avoiding buying too many ultimately useless tool.
I have not yet tried my hand at computer-assisted sculpting for 3D printing, I'll get round to that soon even though I really do not do not get on well with computers...
I started by sculpting busts, and have only recently made the move over to "full" models. Each different model, each artificial category that we classify creations in, have different sets of challenges. I think the most challenging are historical models. Not only are the fans of such models usually very well informed concerning their chosen periods, but often the subject to be sculpted is very well documented. So the sculptor has no "wiggle room", he has to re-create what once was a reality and that is a lot harder than creating the meanest toughest looking futuristic alien, or anything else, where the imagination of the observer does half the work for the sculptor.
Most of the time I sculpt from a more or less detailed concept, but sometimes I start blind and just build my wire skeleton and dress it simply seeing where the putty takes me. In this way I concentrate more on the use of the tool in hand rather than on the model. I have found this to be very useful and liberating: without an obligation for a specific end product I can explore different uses of tools and allow lady Serendipity to work her magic. In effect, this is a lot like how I deal with creating my own concepts & scribbles.
I think that it helps a lot that I was a painter before turning towards sculpture. After years of getting used to how a brush moves over the volumes, details, and textures of a sculpt I think I have a stronger understanding of what can and can't be offered to a painter. Also, it gives me a point of reference when trying to push back those ideas of "can and can't be done"...