I started boxing at the tail end of Burning Crusade.
Did my RAF, and just barely leveled shammies to level cap before WotLK.

So my first boxed instances, as the whole group were WotLK.
I did questing to level.
And ran dailies for gold, to upgrade my tank asap.
Decided on Prot Pally Tank, 4x Elemental Shaman.

Died a bunch, doing heroics on the six or seven bosses which were suggested as doable with a fresh team.
Not sure the exact number of deaths.
Pretty sure there were 3-4 heroic bosses that fell on the first or second try, having read the strategy on this site.
Within a couple of weeks (likely helped by AH gear upgrades, via Dailies) all seven bosses were on farm status.

I gradually added gear to that mix.
Also started doing Dailies on three separate teams, for close to 5k gold a day.
Somewhere in there, I dropped one shammy for a destro warlock (replenishment and 13% extra spell power); even with a toon less than half geared, the team as a whole significantly improved and tougher encounters were easy.

Eventually did all heroic 5-man content except Oculus.