One of the things that makes flirting fun is a sense of humor. Avoid religious jokes, political satire, off-color humor, or anything that might offend. I know that sounds tricky, but be sure you think through everything you say before you say it. Never link to nudity or partial-nudity either, even if it seems funny to you. That’s a good way to scare someone off.
Silliness (like slapstick comedy) is usually best. You’re also safe to make fun of yourself–but be careful you’re not just dissing yourself.
If you’re flirting online, funny/silly links make you seem like a humorous person, even if you’re not the person who created the humorous site to which you’re linking. It’s weird how people connect your personality to the links you provide, but that’s exactly what happens.
Try to keep jokes clean, too. (Rudeness and swearing often hurt your standing with the opposite sex, rather than help it.) One comedian you might study–really take the time to look at his technique–is Jim Gaffigan. If you follow him and people who like him, you’ll find more links to stuff that’s clean and funny.
Also if you’re texting or chatting online, a winky sign is a flirty thing to include in your text. If you don’t know how to make the winky emoticon, it’s a semicolon ; followed by a closed-parenthesis ). Any time you think you’ve said something clever, follow it with a winky emoticon (but be careful not to go overboard with these).
Finally, consider inviting someone you like to an online chat group. Look for things you and he/she have in common. Do you both own a parakeet? There are chat rooms for that. Do you both like to cook? There are chat rooms for that too. Do you both like to read? Goodreads offers numerous book-talk groups.