I love making icons, here's one I made the other day.
It's really about getting a good and unique idea for the icon, you don't want to stick to the basic and clichéd types of icons. Use your imagination! From there I find it's more about working with the pixel space you have available to cram in as much detail as you can without making it look squashed or unprofessional, and there is definitely a fine line in that regard!
My first step is to brainstorm some ideas for the icon, I'll explore different avenues of representation, angles and themes. Then I will do some hunting around online to see what's been done already and specific techniques they've used to bring out extra detail. It's important to differentiate your work from everyone else's, if you can, so copying designs at this stage will serve no real purpose unless you're still learning about the software you're using (Illustrator/Photoshop/etc) or working with designs at the pixel level. And if you're at that level, then you really shouldn't be offering icon design as a service.
It's important to develop your abilities within creative thinking and planning, but it's not always going to be possible to come up with something 100% original now that we have a global economy. I use Google Images and
http://www.thenounproject.com for my research. You can filter Google images to only show icon sized images, which usually helps. From there I'll review and revise my initial selection of sketches and then replicate it in vector format.
If you want to practice, use a random word generator and try to make some icons for the first word it gives you. If it gives you a word like juxtaposition, you might want to generate a new word!