First and foremost, painting miniatures is a process, and it's good to just start. Don't be discouraged by initial results and you'll find that you'll start to develop techniques and gain experience with paints and brushes.
Reaper paints are good, and I've had good use out of Vallejo as well. When you use the paints, squirt or pour some into a cup or lid as Windyridge suggested as it will save the paint bottle from drying out. I've only used water-based acrylic paint so I can't speak for other types. Depending on how quickly you go through paints, you could use a 5mm stainless steel ball bearing to drop into an old pot as an agitator to loosen things up.
Have a small bowl or jar of water to clean your brushes, and a paper towel to dry them by "brushing" them across the towel. Don't soak the brushes in the paint. That can leave paint stuck in the fennel which will skew the bristles into non-cooperative ways.
As for brushes, you'll want a base layer brush with a slightly bigger head for large area coverage, and several fine-point brushes for detail work. Paint in layers from the bottom-up, large to small. That means you layer on the base coat first, which could be the primary color on clothing or armor. Build up from there, adding a darker shade or a dark wash to the recesses, then a lighter shade on the raised areas to give depth. Many fine details are raised above the larger areas, so work on them last.
Along with the wash recommendation, there's the dry-brushing technique to really bring out those highlights. The basic principle is that darker colors are in the deeper or lower parts of the miniature, while lighter colors are more towards the outside surface.
The funny thing is that miniature painting is not designed to be a replica of what the person or object would be in true scale; it's to trick the eyes into believing what they see is a replica, so you are trying to provide contrast for the details and let the person fill in the rest. Of course, there are those master-class artisans out there who are experts at blending and shading and other painting techniques, but if you're just starting out don't look at those and feel that you have to do what they do.
These examples were painted using the above principle. For the single model, I layered a darker shade of color to the large areas, then a lighter shade on the raised surfaces to give the illusion of depth as you can see in the hair and fur cloak. The armor was basecoated in a dark grey, then dry-brushed with silver on the raised surfaces. I did not use a wash as this was painted before I started to try out that technique.
I used the same techniques for the group of models, and this time hit everything with a wash. You can really see the areas where the wash collected in the recesses and crevasses to provide contrast and bring out all the details. For painting a squad, I recommend an assembly-line method of painting the same areas with the same color one after the other. By the time you finish with the last model, the first has reasonably dried enough that you can apply the second color, and you repeat the process.
