Choosing a good looking style for your forum is a very important factor that can deflect on members joining, you would want to choose a theme that would suit all members but that is hard to do. Styles are classed into two categories... dark and light, in general dark themes are mainly used for gaming, music forums etc and light themes are generally used for a professional look and feel.
In choosing a theme for your forum you need to consider these points…

1. What colors would suit your topic of forum. E.g. Football forum would be a green style to represent the grass or a red style for a Manchester united forum.
Just by picking different colors from your topic can lead to a great color scheme that would suit your members perfectly.

2. Give your members choice? Try and install more than one theme ideally one dark and one light, members like choice and freedom to choose what they prefer.

3. Ask your members! It’s always important to ask your members first instead of jumping straight into it, remember members are the most important do what’s right for them .

4. Start a poll, poll’s are great for deciding certain things, you could make a poll with a few different styles and ask the members to vote and the one with the most votes give it an install or even the second most popular too.