For those without unlimited power, here is how I would play:

There are SO many portals now, and many of them are unclaimed. Try to make it a point to take over 1 portal per day, either by force, or finding an unclaimed one.

Destroy portals -randomly- it feels great and they don't see it coming. Even if you only put L1 resonators in it's place, you gained at least 2350 AP from the venture. Level 4 agents can destroy a level 6 or even 7 with a little determination. More links = More AP = Leveling up faster

Small weapons can make a big boom if used properly! L1-5 XMPs are best used directly on top of the resonators. If the portal isn't at full power, SMASH IT! Remember, portals drop their links if there is only 2 resonators left. If you can't destroy it, cripple it. This is where you will gain a ton of AP.

Farm off of enemy farms- it drains the XM in the area, and each portal you get to has enough XM to at least allow you to hack again. Don't wait for the Big Dogs to go out and Flash Farm, play for yourself! It doesn't gain AP as fast as going in a crowd, but it adds up faster than not playing until you go out with a crew! (It took 6 months, but I made L8 solo)

Recharge something every chance you get. I drive for a living, but I gain 1000-2000 AP per day just by recharging. Open your scanner, drive, and find a portal to remote recharge when you stop. Every little bit helps!