With the PoWar mission gnoll shroud, when maxed to 5/5 you will get 153-204 ish AC depending on your class (based on your classes AC Soft-Cap, ie Int casters + Druids get the top end)
The more outside help you can get the faster it will go, some ways to go:
If you absolutely cant get outside help, try to get buffs in GL and stuff like Temp, DS, Regen etc, if you can't get these then your best bet is to shroud to level 5 and just zerg some newbie yard/zones
If you can get Mage + Shaman, Druid, Ranger, Cleric:
With all pairs but the Cleric you can just get Regen + DS buffs and go to town on newbie yards or the Warrens (they run)
With the Cleric you can Viral RDS and zone the cleric out, with pathing mobs this can viral debuff basically the whole zone, RDS works in a special way in that it attributes the damage to who gets hit from the mob, so the shroud has to be the one being hit to get kill credit
Other method is using level 70 shroud and having people who can zerg Grounds or the Hatchlings in HoFC, maybe Xorbb halfling army mission etc, this method is probably slowest though since it takes longer to kill everything
Fastest way is doing your normal DS PL's, buy some Oil of Fennin Ro's (you can use a Bard if you want to flip them a lot, Bard box with ftp will constantly out level your shroud though so it makes it annoying to do this route)
Normal DS PLing is simply, pull a huge train on a big toon (Bard, Sk, Pal work good for solid AE aggro) without a weapon in main hand ( you don't want to Riposte), once you have ok aggro, right click the oil on the mobs, then spam sit on the big toon PL'er, a good spot for this is Undead in Crescent Reach, these repop super fast, use level 15 shroud
Shrouds work like Evolving items do, the higher the con the better the EXP, the less in your group the better the EXP.