There are many different clays available, best advice, try them all and decide what works best for the results you desire. A few companies even give tiny free samples. I chose medium Chavant (non sulphur) because I love the way it feels and work with it warmed in my heat box (easy to build) and when really warm gives wonderful texture wiped with an old scratchy wash cloth. It is not a water based clay so stays workable if just covered for months. Holds a very fine edge when cool.
Once I got the basic anatomy done on the buffalo I had more fun just imitating their hair in hot clay and loved the results. You can drag your tool whether it be wash cloth or wad of paper, wire brush or anything that leaves a good design on your clay.
I can't speak for anyone else but I have one bad habit I have tried to break myself of and not succeeded. I have a tendency to work on specific areas long before my beginning structure is laid. Bad habit! I love eyes so have a tendency to jump the gun and focus on them. I also tend to work on one side until it is finished and exactly the way I want before going to the other side. I have always assumed good artist should work in the round balancing the piece as they work.
If there is an interesting texture involved also I try to get it just like I want. One of the most important things I have learned is that "hey you did it the first time you can scrape it and do it again but better". I always hated throwing a piece into my clay box until I realized I was not happy with it for a reason and to trust my instinct. An artist has to learn to trust their eye and if you have worked on a piece too long try covering it up for a month and working on something else then go back and things will really pop out if incorrect. I only do pieces I have passion for so in that case you know your subject upside down and backwards and your brain will tell you when something just is not right...it is like a computer it will eventually figure it out. (Sometimes it is at 2:00 am and you sit up in bed with the answer). I have a friend that says things pop out to her if she looks at it upside down.