I've done this sort of thing probably several dozen times so far. Your biggest concern, unfortunately, needs to be ensuring safety and overall pleasantness of encounters (awkwardness is okay and to be expected, and goes away as you get more practiced). So the guiding principles are the same ones that you'd use to engage with people you first meet in real life.

These are my informal rules and I think a lot of people already use them in one form or the other. This assumes that you are either oversubscribed (more people reaching out to you than you reaching out to people) or equal-subscribed (about equal, and at a kind of peer-peer status). If you are under-subscribed, I suggest you start building up more of an online persona before getting serious about offline-to-online interactions. Otherwise you'll be on the wrong side of these rules and get a very low response rate to your reach-outs, with more potential for unpleasantness.

Triangulation Rule: I recently proposed a "triangulation rule" -- that you should wait till you encounter somebody in two different online channels before trying to meet them offline (example: Quora+ comments on some blog). For women and other vulnerable groups with more reasons to be cautious, you may want to make it 3 channels. Diversity of channels gives you a chance to see a person in 3D basically, against different backgrounds.

Length of Interaction Rule: I'll add another rule if you want to be even more cautious: don't offer or accept an offline meeting request unless you've had multiple online interactions extending over several months.

Intimacy Capacity of Channel Rule: But these extended, multi-channel interactions should not be escalating above the trust level of the channel itself. That's a danger sign. If someone is getting to a level of intimacy over email that you'd normally associate with face-to-face, first, back off and stop enabling it, and second, develop behaviors to channel-limit the intimacy of what you share/connect over. Sometimes people over-load the intimacy capacity of a channel due to lack of online experience. But quite often it is either a conscious or subconscious desire to hide things about themselves that would be relevant.

Train Your Radar: But overall, you want to just start developing a hyper-sensitive radar for dangerous or unpleasant types of weirdness. Lots of people on the 'Net are weird, in good and interesting ways, so you don't want to filter those out. But some people just send off all sorts of red flags simply in the way they communicate. I first noticed I was developing this sensitivity when I was learning to tell genuine blog comments from spam comments (and later genuine blog guest post requests from splog-requests). The language is just slightly 'off.' Later, I started developing sensitivity to "offness" in obviously real people as opposed to deliberate deceivers like spammers/sploggers.

Application

I've now done enough online-to-offline encounters that I often ignore the first 3 rules and go solely by the "radar" rule. But I don't recommend doing that until you've done at least a dozen. It simply takes a while to train your radar so intuitions can take over. Until then, the first 3 rules will ensure your safety.

There are other principles that apply in special cases (asymmetry of visibility between the two parties, the potential for a sex/money/power transactional angle and whether each of the parties wants that angle...).

I'll add one rule for the encounter itself. If in doubt, 3-way it. That is, take along a friend, ask them to bring a friend too, or make it a group event etc. Even if there is no good reason to be suspicious, this helps make things less awkward. I've done this a couple of times simply for managing schedules better, but it always has the added advantage of creating a richer conversation.

I hope I don't need to mention the obvious rules: don't reveal things like your home address or phone number if you don't feel comfortable doing so. Meet in a public place. If you are female, and can't find a chaperone, carry mace and make sure you're not followed if the encounter is unpleasant. Basic rules of engagement here.

One what-not-to-do suggestion. Don't play hard to get or implement arbitrary "dance for me" rituals to gatekeep access to your time/attention. Managing a pipeline of interesting conversations that are heading towards a IRL interaction can add a few hours of email time to your week (unless you are a genuine big celeb). Just put in the time. Keep it normal, friendly and peer-to-peer. Playing games only lowers the average quality of who gets through your defenses.