Can anyone tell me how to paint polka dots or stripes on wooden letters?

My boyfriend gave me a large B letter for me to paint. I really want to do cute designs on it but I do not know how. Things like stripes, polka dots, swirls? Anything really that will nice. The problem: I have done the base coat and did three good layers so that it has a firm background. Now how do I put designs on it? I have paintbrushes of all kinds, 5 base colors, and some stencils(peace sign, swirl and alphabet). I cannot afford to buy anything extra and I am afraid to free hand it. Any ideas?