Forsythia looks best when it's allowed to grow naturally into a big arching shrub. Those long branches are the first of many. I wouldn't prune at all. In a few years, it'll be a big beautiful flowery thing.

Yes, it looks best with the long arching limbs, as carol says.

It does need a good amount of sun to do best. Here's a link to the shrubs forum.

Here is a link that might be useful: Shrubs forum