Sometimes, you just want to make sure someone's thinking of you when you're not around. But making somebody miss you is difficult--push too hard and you risk coming off as needy or desperate. Here are some tips for staying on someone's mind, in a good way.
The first step might seem counterintuitive at first, but it works: Stay away for awhile! As the old saying goes, "I can't miss you if you won't go away." If you're always around, you can't be missed. So, even if it's difficult, make sure you give the person you want to miss you (we'll call them Person X) enough time and space to wish you were there.
Stay busy. The next time you talk to Person X and they ask what you've been up to, the last thing you want to say is "Nothing." Instead, you want to be able to tell them all the fun things you've been doing with your time. You want to show that you're an interesting person with lots going on in your life, so Person X thinks, "Hmm, this person knows how to have fun, we should get together," rather than "This person is boring, and there's no need to make plans -- they'll always be around if I want them."
When you are together, ask about memories. "Remember that time we went to the grocery store and you juggled the kiwis?" or "Remember when we went to the beach and had that cookout?" Obviously, you don't want to bludgeon the person with do-you-remembers, but do bring them up from time to time. Doing this reminds the person of how much fun you have together, and it gives them something to think about when you're not there.
Finally, just plain be good company. It's easy to miss someone who's funny, thoughtful, and enjoyable to be around. If you and Person X consistently have a wonderful time together, they'll miss you no matter what.