Lots of good advice already I see. 
I’m going to split mine into two categories with some overlap - tips for people going on a skirmish and tips for people who organise/lead them.
Tips for skirmishers:
- Preparation is key.
- You can get really good bang for your buck on the equipment front if you spend a few small coins on cheap but effective items. Even though I don’t play a physick I always carry a few herbs to cure things which commonly affect me or my mates (one to cure a broken limb, some vervain for hit points etc). And often a mana crystal so someone can mend my weapon. These are all cheap as chips compared to potions or artisan items, can be bought very quickly and can save your life. If you don’t use them you can sell them on or save for later, as they don’t go off.
- Stay alert. Once you are on a skirmish the environment is live and there will be no ‘time outs’. So you need to keep your eyes open at all times. Just because you can see an enemy unit ahead of you doesn’t mean there aren’t more and just because you have won the objective doesn’t mean it is all over. Some barbarians particularly like to use ambushes and those can be deadly.
- Know what your objectives are. Know what you have to do to achieve that. Even better if you also understand what the enemy is trying to do too.
- Use your time effectively. With such small teams going on skirmishes you are never a useless body. Even if it seems like everyone else is busy, there is always something useful you can be doing (fighting, watching for threats, bringing the wounded to a healer etc etc).
Tips for skirmish leaders:
- Preparation is key. Even more for you.
- Know what the skirmish is about and what you have to do to achieve victory. I like to brief all my skirmishers on this so they have the capability to use their initiative. Then before we go through the gate I will get them together and quiz them - ask them questions from the briefing to make sure they completely understand and are ready. This also lets them ask any last minute questions.
- Have a good second in command or structure to your people. If you have this in place then you can swiftly order a group of people into action under one of those officers, pull of tactical moves etc, without having to create a sub-unit on the fly. Plus some back up if you get taken out of action.
- If your troops need particular gear for the mission, tell them when you recruit them so they have time to source it. Make their lives as easy as possible here.
- Talk to respected experts. Other skirmish commanders, your generals, the Hospital staff etc. They might have faced similar enemies (often that same day if a lot of missions are going into the same territory). Learn from their experiences.
General:
- Aggression and initiative win fights. All things being equal, the side which attacks and exploits opportunities will win.
- Many skirmishes are roughly even fights. On that basis I have a rule of thumb that you can decide what to do based on a quick glance around you. If you are outnumbered where you are, it hopefully means your mates have got the enemy outnumbered somewhere else. Keep calm, threaten the enemy and help will be on the way.
The flip side of this is that if you find you outnumber the enemy in your immediate zone, you have a responsibility to push hard and capitalise - your good situation has been paid for by your mates taking on more of the enemy, so you owe it to them to capitalise and then go to their aid. - If you feel like your position is bad, showing fear can get you all killed. I find that when the enemy are confident they are more likely to push hard and overwhelm you. Thus I strongly believe in the power of psychological warfare; rather than showing I’m worried, I’ll try to push, making attacks against as many individual enemies as I can so each of them feels personally threatened. That can give them pause and buy you either room to maneuver or time for a rescue.
- Use the terrain. If ground is open, make sure you hit exposed flanks of the enemy. If in trees or hills, use that to split the enemy and kill them in detail, or stop a larger enemy ganging up on you.