We all know the huntsman is pretty much a totally different class than the traditional sniper. (Of which I'm horrible at, I just have to get that out in the open for the sake of posting in the section of the board). The huntsman fits the "Support" role much closer than the sniper because of the support damage and mini crits it brings to a team.
LOADOUT
I'll start off by saying there is no excuse for the SMG unless you're in a tiny team (in which case you'd be better off playing a different class like a medic), or maybe playing in arena (if anyone does these days).
The Jarate is what the huntsman is about. The huntsman allows the sniper much closer to the action to deliver his mighty delivery of urination domination where it is needed most. Use it, love it, it is the reason you are on the team.
RANGE
The huntsman is a good weapon at mid range, and in a pinch close range because the more you play the more you'll be suprised at the number of scout headshots you get. Especially running and hiding in a corner waiting for the scout to come around. That hitbox is very forgiving. Long range? Its just spam with good judgement. As long as nobody knows they're being sniped you might pull off a headshot, anyone standing still is a given. Due to the recognisable sound though don't expect more than one chance before they start doing the anti sniper dance.
POSITION
Behind the frontline, for obvious reasons. Your health is lower than a medics and you know how often they have problems with scouts. NEVER venture around without protection. Your job is to make sure battles go favourably for your group using crits and landing arrows in high health targets. Hopefully killing medics too, it happens but due to the positioning and range of good medics it can be hard. If they know you're sniping them they'll also dodge like crazy and it'll turn into a whack a mole game. And if you aren't doing damage at least to someone, you aren't useful. A regular sniper knows he has to pick off a target in one go, you have the advantage of a lower charge time and easier body shots so your DPS to the other team can be much higher.
Never be afraid to run for cover, ever. That jarate timer is er....golden. Don't die when it's almost ready. You can keep pulling back putting more distance between you and the other team. You can still spam from range and get lucky shots. Remember, the hitbox is forgiving.
You will however die to scouts. Alot. So as a final revenge, make sure the last thing you do in this world is cover them in a reminder of you. Your team will thank you for the mini crits.
JARATE
The number of sucessful jarate throws you get is as good a measure of your sucess as a medics ubers per life. Because it's basically a semi kritz. Aim for targets your team can easily reach at that moment, and announce the hit to your team. Mostly it'll be frontline medic partners, unlucky scouts, or best case a group of people capping a point.
Protip: Landing a jarate into point B at the right angle through the window when a few people are capping, then telling the demo or soldier on the roof to go blast away, is the most fun you can have with your jar hands down.
If spies are a problem, you know what to do. The voice responses are reward enough, but alot of the time you'll need a buddy to chase the marked spy down. With no SMG its can be hard to charge your bow in time to catch the spy.
Jarate spells big problems for heavies, but don't bother. Your bow headshots will be more useful. Your main targets will be the enemy soldier/medic pairs giving an easy time for yours.
Keep your team informed about when your jarate is ready, but be careful. Jarate DOES hit your allies, it does NOT pass through. That means you need a clear shot, and your enemies need to be in a fairly easy to hit position for maximum...spray.
THE HUNTSMAN AND YOU
Most of your kills will come from people not focussed on you. Scouts chasing down someone else in a straight line are good targets, advancing heavywieght classes are nice targets when they aren't bunnyhopping to avoid being headshotted.
Priority targets, soldiers on the ground are slow moving and fairly easy to hit at mid range, you can wear them down very quickly with half second charged body shots or quick head shots. Watch out for rocket jumping soldiers though, if they close you're as good as dead. Same with demomen, but thier spam at long range is deadlier than your spam, so you need to watch out for stray grenades AND sticky jumping.
Again, your job is to wear down and provide general DPS, like a demoman but your damage relies partly on the team taking advantage of your mini crits. The difference is your headshots can pick off targets more suddenly.
Don't underestimate luck either, the number of times I've aimed for one person and another walks infront of him taking the headshot is suprising.
REASONS FOR TAKING A HUNTSMAN OVER A SNIPER
Well you'll kill less medics, but you will wear the team down much faster making the medics job twice as hard. Huntsman is generally easier on defence because you can coat an emerging team with jarate then take advantage of the sudden retreat. The enemy will spend alot more time hiding behind cover because of you, which basically takes them out of the game for a spell.
I think the huntsman role is more forgiving than the traditional sniper, but just as useful.
FINALLY: I have a fair few hours on the huntsman, almost all of my sniper hours, however I don't consider myself pro at it at all because my main is the soldier and I don't ever intend on putting too many hours into sniper. The main reason I wrote this is to get people talking about the huntsman playstyle seriously. If people disagree, good, they can write about the way they play it. I think the huntsman DOES have a place in high level play, even if luck is sometimes an element in its aim. Huntsman skill is about maximising the chance of that arrow hitting that target. And piss.