Shorter Content or Longer Excerpt with Pictures

I would like to display partial posts (with pictures) on the main page, the lists of posts on category pages, and similar pages displaying lists of posts. I tried using the excerpts, but they are shorter than I would like and don’t display any images. I used to use a theme that automatically gave me excerpts with pictures and never used the more link on any of the posts, so I would like a solution that would work without using the more link.

How do I go about truncating the posts displayed or enhancing the excerpts to get the desired result?