Took down my first portal today. I'm only a level 2, so I think I over extended myself going after the local portal which was level 4. Took 15 minutes hammering it with L1 xmps at which point I ran out of xm. Ran to the nearest portal and recharged, went back and finished it off.
It lasted 5 hours, but at least I'm 1/3 of the way closer to level 3. Good fun.
I've been largely experimenting with different things. In Glasgow, linking portals seems to have worked efficiently mining ap. They're close enough to easily get portal keys and change hands frequently enough that links are not always fully populated.
Any other tips for getting ap if you're lower levels?