Small details always look so impressive and, contrary to popular opinion, are very easy to accomplish. Study the old masters and check out the tiny details. You will be surprised to see that up close the details are "blobs" of paint and hardly ever have perfectly straight lines. It is the application of color that creates detail and sharp lines.
One of the most important factors is having the correct brush. Not always is the smallest brush the best. Tiny spotters require much patience, steady hands and many, many brushstrokes. A #2, #4, or #6 round(depending on the size the project) will easily apply base color as it provides a sharp point to outline the shape and a fat belly to "fill in" the base.
With the same brush use color to add basic details and create dimension. Depending on how small, blending is an option.
The final details are what the eye will perceive. Use an #18/0 mid length or script liner to lay in these strokes. Because the subject is small, less is always better. Just a couple strokes will add amazing detail. Too many strokes will become too busy and tedious for the eye to interpret.
Don't over-think or over-work details. Add a few strokes, sit back and "look" with fresh eyes. A great secret to viewing is to use a mirror. Looking via a mirror points out any weak areas almost like magic.
Eliminate the negative thoughts about painting small. Relax and enjoy painting small with a new attitude. You will find out it really is fun and easy!!