On most keyboards, this is just a matter of placing the key in the right place and pushing down. You'll know when you get it right. Test out the butt...
I found a great keyboard in our junk pile, a Microsoft Natural Ergonomic Keyboard. It has a comfy layout, but there was just one problem. The N key wasn't too responsive. You had to really bang on it to get it to register.
Naturally, this wasn't going to work for regular typing, but the fix for it was easy. Here's how to do it.
Step 1: Pop out the key
Use a flathead screwdriver to get the key out. Just get the tip of the screwdriver under the key and push down on the other side. With a bit of leverage, the key will pop right out.
Step 2: Get a piece of a straw
Cut off a little more than an inch of a clean plastic straw.
Step 3: Fold and insert
Fold the straw in half lengthwise and insert it into the bottom of the key. It should now be sticking out quite a bit.
Step 4: Trim to fit
Cut off the straw so that a few millimeters are sticking out. You now have an enhanced key that sticks out more and will be better at engaging the button inside the keyboard.
Step 5: Put key back in the keyboard
On most keyboards, this is just a matter of placing the key in the right place and pushing down. You'll know when you get it right.
Test out the button and see if it's responsive now. If it's working, but it feels a little stiff, then pop the key back out, trim a tiny bit more of the straw off, and put it back in.