Bad spelling and grammar, slang and internet-speak are all off the table if you want to get the best chance of a reply to your message.
Use a spell-checker, but actually read what you wrote before you send it!
The exceptions here are things like lol! or haha! as these show that you are easygoing and fun. Using these actually increases your chance of a reply!
Tone
Keep it light and casual - write as if you were speaking to this person face to face. Try to convey your sense of humor, but keep it friendly and polite.
Leave room for a response
Ask a question as part of your message, or make a joke that the other person can respond to. Whatever you do, if the site has an option for ‘poking’ or ‘winking’, don’t do this as a first message!
Be interested in the other person
We don’t mean interested in a date, they know that already! Show that you’ve read the person’s profile by asking about something they’ve written - preferably a topic of interest that you share. This shows the person that you’re potentially compatible, and invites them to talk about something they love and enjoy. If they’ve mentioned that they loved Paris, ask them their favorite thing about it.
Be careful with compliments
It’s tempting to comment on someone’s photo, but doing this will typically get you ignored. If you want to compliment them make it about something they’ve chosen, like a funky haircut or cool shoes.
Showing that you like someone’s choices goes over much better than complimenting an aspect of their appearance that they have no control over.
Don’t mention any body parts, even eyes.
Don’t use adjectives like ‘hot’, ‘gorgeous’, or ‘sexy’, either - it’s over-familiar, and feels more like cat-calling than a friendly, casual first message.
Pick a good greeting
Here’s the skinny: saying ‘hi’, ‘hello’ or ‘hey’ will hurt your chances of a response. Instead use informal greetings like ‘how’s it going’, ‘howdy’, or ‘what’s up’. These set a casual tone, while remaining friendly.
And lastly…
Don’t give up! If one person doesn’t respond, don’t take it personally. There are plenty of other people out there, so put your best foot forward and keep sending out those messages!