A first message with attraction and respect
You can express attraction without opening with graphic language or a demand. A strong first message shows that you noticed the person and gives them an easy way to respond.
Use something specific from the profile
Refer to an interest, a shared preference or the kind of dating they describe. Keep a compliment simple and personal rather than reducing someone to a body part. A short message is easier to answer than a long explanation of everything you want from a stranger.
Ask before taking the conversation further
Someone's photo or presence on an adult dating site does not mean they welcome explicit messages. If the conversation becomes flirtatious, ask whether they are comfortable talking about sexual preferences. Match the level they choose. An enthusiastic reply to a compliment is not blanket permission for sexual content.
Leave room for no reply
Send one considered message and allow time. Avoid repeated prompts, guilt or insults when there is no response. You cannot know whether someone is busy, uninterested or no longer using the account. If they decline, a brief courteous response is enough; the conversation can end there.