Not very hard, just time consuming and boring as hell. First, the 1,000,000 exp.
Get a group of 6 - 8 (4 works but takes forever), make a Ranked Armored Front match on Meltdown.
Have the team the starts at point 5 cap 5 - 4. Team at point 1 caps point 1 only. Team that started at 5 makes point 1 neutral, and then team at point 1 re-caps. Continue to do this till only 7:50 is left in which teams switch. Team at point 1 caps 1 - 4 and makes point 5 neutral, etc.
May not sound effective, but this method will net you 350 - 400 points ON AVERAGE which is roughly.... 2,450 - 2,800 exp per game. An hour will net you 10,000 - 12,500 roughly. Do this for 6 hours will get you around 60,000 - 80,000 exp. That's about 15 days (if you want to be optimistic).
Now, you just need to get the various other achievements, which will be extremely easy. You should have quite a few at this point (
Time Well Spent, Control Freak and
Gotta Cap 'em All will be unlocked, along with the other Rank achievements). Just ask your boosting group for help, many people will be willing to help. Here are some quick solutions for the lazy folk:
Flash Dance - Load up any level with a Rocket Launcher and have someone with flash grenades. Whoever is getting killed should get into a corner, makes it easier to be killed, and throw a flash at the killers feet.
City Planner - Just destroy doorways, fire hydrents, signs and the bus stops. There are about 15-20 if I remember correctly, so just grab them when possible. Mech required.
Demolition Expert - Easiest done with 2v2. Have whoever is going for the achievement run to the nearest demo site, it doesn't need to go off, just be planted. If the other player spawns with the charge, have them commit suicide, they'll drop the charge. Best done on Conduit.
Dastardly Disarmer - Same as Demo Expert, in principal. Decide who'll disarm, rush to the site and disarm it. Also, do this on Conduit.
The Mad Capper -
Bad Robot - I suggest using bananas solution for the most effective method.
Gets very boring, don't relax, I laid down and nearly fell asleep many times, sit up and you won't fall asleep. Put on music, or something. Anything to keep yourself awake. Best of luck.
EDIT: Please note you must have ALL other online achievements, City Planner, Flash Dance, etc.
EDIT 2: If you're going to vote negative, please leave a comment and I will add whatever information is needed. Thank you.