Earning a merit badges is one of the best experiences in Scouting but it isn't as simple as it looks. It often requires a bit of planning and research. 

The most important thing to realize is that not all badges are the same difficulty. Some are hard and meant for older boys with plenty of experience. Others are simpler and feasible for scouts who are just beginning. Who can tell you which is which? Your scoutmaster (or suitable assistant.)

Here are the steps:

1. Choose a badge. There are hundreds of them and you can read about them here, here or here. 
2. Read the requirements. Ask yourself, "Is this something I'm ready to try?" It's good to push yourself-- but be realistic. 
3. Ask your scoutmaster (or suitable assistant) for a blue card. 
4. Find a merit badge counselor. There's a partial list on TroopTrack. Others can be found at summer camp or by asking around. Your scout master or other leader can help.
5. Approach the counselor by calling or emailing. 
6. Be ready for the counselor to ask you to do some preliminary work. I've found that filling out the worksheets are a great way to make sure you've done the basic preparation. 
7. Some of the most difficult badges require you to practice something for hours or even months. Don't start this without talking to the counselor first. 
8. Some badges only require one meeting with the counselor. Others require many. Be ready to do what your counselor asks. 
9. When you're done, make sure to get your conselor's signature on the blue card.
10. After you get the badge, KEEP your part of the blue card. You may need it later if records get misplaced.