[Hammarling]

I've never met anyone for BDSM reasons, but i have met people from the internet.

Trust, time and safety. Basically what others have said above.

Trust - Do you trust this person? If i wouldn't tell them something personal about me (something no-one but my friends/family would know) i'm not ready to meet this person. The people i've met from the internet, i've really trusted for a while before we met. They've known most of the details about me, the same as any of my real life friends i'd go and meet.

Time - How long have you know them? And i don't mean when did you first message someone. But how much do you interact? There's online friends i've known for years, but we only exchange a message once everyone month or so. Despite knowing them for years i wouldn't meet them. But i've got friends i've only known online for a couple of months, but we talked every single day and i really felt like i knew them.

Safety - You'd think it's obvious, but just look at the news and you realise some people don't have common sense.
Make your first meeting somewhere public, like properly public. Not an alley behind a restaurant public, but in the restaurant public. I've taken this to an extreme and met people at sporting events where there are thousands of people, but i knew i was safe.
Tell someone you're going. Make sure someone knows where you will be, and that if there is a problem you can contact them.
Have an exit plan. Just in case they are not what they seem, have a plan to leave.
Take a real friend. Ok for bdsm this might take some explaining to a friend, but an extra person there will make you safer. If it goes well you can always leave them for some privacy.

And just really talk about it with the other person first. So you both know the plan, the timings. If you're anxious tell them, they can try and help.

Finally, if you don't want to go offline you don't have to. No-one can force you to meet up for real.