Clean your figures well with a detergent and water. If plastic, you can paint directly or opt to prime first then paint. A resin or metal figure must be primed first. Everyone has a persoanl favorite and it depends on uniform colors etc, but I use either a flat white or flat light grey automotive enamel primer. I then paint an acrylic underbase and either continue to use acrylics or switch to oils.
I have come to believe that if you can put it on a brush it can work. I have seen everything from guache to oils used and with stunning results.
My favorites are the vallejo line of acrylic paints, andrea (also made by vallejo, just contracted to andrea), tamiya paints and model masters. Although I have used Americana and deso art acrylics to good results. Winsor & Newton are my favorite oils. Expensive but smooth, good pigment and blend nicely.
Others use enamels and there are several good companies out there that have a myriad of paints. I wish I had a definate answer for you, but the best way is for you to continue to ask and experiment till you find a "paint system" that works for you and gives you the results you are looking for.
Don't try to cover the surface completely with one coat. You will have better results by doing a couple of light coats and that will yield a good solid coverage and smooth base. From there you can then build up your highlights and then your shadows (it's easier to paint dark over light than it is to paint light over dark).
If you use enamels for a base, allow them to cure thoroughly before getting in and trying to use washes as the solvent will affect the base coat. If I paint in oils, I use an acrylic for an underbase and this way the thinner solvent won't damage the base coat. If I continue to use acrylics I make sure that the previous coat or work is dry and cured so that if I have to "work" an area it won't damage the previous coat. This can be 24 hours or longer dependent on conditions (hot, cool, dry , humid etc)
Good luck.
Mike
"Imagination is the dye that colors our lives"
Marcus Aurellius
A good friend will come and bail you out of jail...but, a true friend will be sitting next to you saying, "Damn...that was fun!"