I know that a lot of people get stuck when it gets to making cards for guys. According to my husband the 'rules' are quite simple.
1. No shiny stuff
2. No bows (but knots are ok)
3. No flowers
If you're lucky and you're making a card for someone specific and you know what their hobbies / sports / likes are it should be easy to find a focal image. Keep the colors bold or neutral. Usually you will stay clear of pastels.
If you're making general masculine cards, it is usually safe to stay with themes like the following:
* Ocean (lighthouses, ancors, boats)
* DIY (tools)
* Men's clothing (ties, men's hats etc)
* Geometric shapes
I'm sure the list can be extended but this is a good start and I found that as you start looking for one image, it makes you think of something else that's appropriate!
Here are some masculine cards I made with Father's Day in mind:
Digital focal image: Meljen's Designs - Purchased at http://whimsystamps.com/store/index.php?main_page=product_info&cPath=13_18&products_id=1035. This was colored with normal coloring pencils.
Digital image: http://www.clker.com/clipart-26399.html
"Dankie, Pa" is "Thank you, Dad" in Afrikaans.
Digital paper: Go to stamptv's Freebie Page: http://stamptv.ning.com/page/freebies-2 - Scroll down to "Jersey Shore" and download the ZIP file.
Digital image: http://www.clker.com/clipart-small-boar-rowing-beside-lighthouse.html
Same digital paper as card above.