1. Use mercs marked with (*). Can buy them in Galadon.. They counts like a groupmate.
2. Some people can solo rank anyone. If you do not know how - assassins/rangers/paladins - your choice.
3. Forget about cabals that requieres interactions/immteractions and player killing. i.e. - you can joins Fortress as Acolyte, or Empire. But can not become maran or scarab.
4. Use quests.
5. Use exploration/obs to cover gaps. i.e. for me, personally there is a gap for a goodie ranger between 27 and 30 level. Trolls, drows, tresnores are too easy, ugruks too hard.
6. There is a certain quest that gives you dozens of cure light pills. Complete it. They will help you to rank faster.
or...
just do not waste your time. Roll invoker/healer/whatever you like, connect another notebook/desktop/whatever to the internet using cell phone and roll a tank.
Fast rank both characters ceparately up to 10/11 level. It is easy. At 15 go and perfect tank defenses. while your main char do exploration, solo ranking, quests etc.
Then join them back and level up. Keep recall potions for your main. Noone cares about conloss of your tank.
Someone will call that a cheat, Yes. It is.
I had a shapeshifter. I had to rank up with necromancer. Shifter and necromancer - "nice" group. We did talk before join in group and often I had no time to level up with him or he had no time.
It was no multiboxing or multicharing. Different people, different chars, while 3-4 players online. Sure we permagrouped.
IMMs transfered us both to the RoD. Held there for few days. And punished for perma.
So yes, it is a cheat, but they can go to hell with that. Because you will be punished anyway. You will group with the same players if you play in low time. And will be punished for that,