Here is an exceptional resource, if you just started gigging and perform solo. Recently Tom Robinson ran this workshop for BBC Introducing and now he's written up a full-length guide, in which he really digs deep into first steps of developing solo stagecraft.
Obviously any guide like this is a template not a rule book. But I've simply never seen such a brilliant piece, that covers this much ground and includes so much good gigging sense.
I had four additional thoughts (read Tom's piece first though):
1) When you've got your friends in...
If you have a room full of strangers but there's a group of your mates somewhere down the front, it's very tempting to aim your set at them, or even more riskily, get involved with in-jokes or banter, especially because they've come to support you. Resist this as much as possible: the first thing that happens when a performer focuses on friends is that the rest of us, not being part of that, feel left out. Think of it like this: your mates should be the last people you need to win over.
2) Refer to the audience in the singular as much as possible...
This ties in to what Tom says about saying "you" instead of "I" and in fact it's a trick I learnt as a kid from Philip Schofield back when he presented Children's BBC in the broom cupboard with Gordon the Gopher: talk to your audience as if they're one person. So: "It's good to see you, thank you for coming," is better than "It's good to see so many of you, thank you all for coming," as subconsciously each person feels directly addressed. You can't always do it but it's worth getting into the habit.
3) Have a few 'stand-up'-style put downs in your pocket...
You will get heckled at some point. It may be cool, it may be nasty. The easiest solution is always to laugh and be nice in response but with a funny line, remembering you're up onstage with the power of the microphone (and you can say you're the one "getting paid" to be there, even if you're not!). However you might want/need to get nastier and remind them what you did to their Mum or Dad last night. But again, be careful not to get caught up in banter. If you focus on one group or person too much, you leave out everyone else.
4) If the gig is very small, don't be afraid to ditch the stage altogether...
If you're playing acoustic guitar, in a tiny room holding, say, fewer than 40 people and you've got their attention, you may make more impact performing unplugged. People enjoy that extra closeness and somehow think of you as rebellious for eschewing the gear. It's also still seen as a special talent (or 'braver') to play unplugged, where in truth it sounds a lot closer to your rehearsals at home and you can hear yourself better. Only works if the room's quiet though.
Finally, the one part of Tom's guide I find myself (mildly) disagreeing with, is when he discusses onstage monitoring. I'd argue that Tom's own vocal power and experience means he doesn't rely on monitoring as some singers do (me included). I personally would never ditch the monitors and rely on the PA, or ask for the FOH mix to be in the monitors. I also think it's not so important to bring a sound engineer to small pub/club shows and can sometimes be detrimental: the house engineer who works at the venue is likely to do as good a job, since s/he already knows the room. And, especially if you're a support act, it can piss off the house crew, if your engineer starts messing with the desk. Yes, you'll occasionally find duff / moronic house engineers but gigging on a budget, how good really is the friend you're bringing? I find it of more value to have someone smart with you for soundcheck, who simply knows how you should sound - but doesn't want to play with the desk. Your friend can listen from the floor and give suggestions.
Anyway, that's my 2p for now; even having done almost 2,000 shows myself over 15+ years, I found reading Tom's piece useful and cringed at a couple of basic errors I still make. So I hugely recommend it.
Chris T-T is on tour around the UK from April 13. To find a show near you, visit his Live page.