EDIT: nice advice posted from others above while i was writing, so sorry for any repetition.
You poor bastard
Which dungeons are we talking about exactly, and speedrun I guess means pulling lot's and lot's of mobs?
It's hard to say what will work for you depending on your particular gear level, the particular dungeon, how many mobs are pulled, the ilvl of other players, how well tank keeps aggro, etc, but some of these tips may work for you:
- Don't worry about holy until you're comfotable with just healing. Using holy reduces the overall need for healing and makes things quicker when you've got the hang of it, but I found it helped to learn the speedrun without dps-ing first.
- If you can't get a stoneskin up before the tank stops don't worry about it. Stoneskin is a slow cast. You might swiftcast it if you really want (and have swiftcast), but I prefer to save the swiftcast.
- Overcure while learning! Start with a cure 2 followed by a regen on the tank, only if you think another cure 2 isn't needed. He'll take huge damage at the start of the fight because that's when the most enemies are alive, so don't wait for the damage to happen - predict it. It's better to overcure with cure 2 spam while learning, then when you get a feel for how fast the tank and other players will start dying you can ease off, and use regens and medica II's. In the same vein, don't wait for the tank to be nearly dead before popping cooldowns like presence of mind. In a speedrun the biggest damage is at the start when most enemies are still not ko'ed - use divine seal and presence of mind right away if available, since you're less likely to need the boosts when enemies start dying off.
- Don't forget benediction. This is a life saver in speedruns. If the dps are taking some damage and you decided to cast medica or medica ii (slow casts), you might see the tank's life dropping rapidly, by the time cure ii casts it might be too late whereas benediction is instant. Again, overcure while learning, don't worry if you waste your benediction this time - play it safe. later you'll get a feel for whether there's time to cast a cure ii before the tank is killed or not.
When you are comfortable with heal only, you might try adding holy/dps to the mix:
- If the tank is good at grabbing aggro (he likely is), start with swiftcast holy, followed by 2 more holy's. The swiftcast is a great on the first holy (if you have it), because it'll provide an almost immediate stun during the most dangerous part of the fight (the start). While learning limit to 3 holy's as the enemies will be resitant to further stuns and you'll likely want to switch back to healing.
- When comfortable (probably higher ilvl too), you may try pushing more holy's until you know it's the last second, then benediction(to full heal tank), shroud of saints (to get some mana back and drop aggro), switch to healing stance (obviously important), regen (might need a cure ii first), then depending on how fast the tank is losing hp, possibly stoneskin (again to give you more time dpsing) and switch back to cleric stance holy spam. This time be even more careful - if benediction and swiftcast are both on cooldown, don't leave it too late to switch back to healing or even perhaps don't bother dps-ing.
- alternatively, don't start with holy. Try to get a stoneskin on tank before the pull (stoneskin 1 is faster to cast, forget stoneskin ii if everyone will be out of range by the time it's cast) - then, when he stops pulling divine seal + regen, start casting another stoneskin, then switch to holy spam. This will work well unless the tank's hp drops too far before the 2nd stoneskin is up. You don't want to go into dps without the tank near full health since you can't take off cleric stance again for a few seconds at least.
Keep trying with duty finder groups, and don't worry about the criticism / kicks. That's just ignorance, and you'll get the hang of it with practice. Playing with friends is great, but if you want to improve, playing with random players can push you.
Also, just because I or someone else tells you do this move, then this move, then this move, doesn't mean it'll work for you. We may be overlooking the difference in our cast time, healing potency, etc. Try to analyse exactly what caused the wipe (whether yours or someone elses mistake) and consider your own strategy to combat that with all the spells/skills you have available.