I would guess over-extrution and perhaps you're printing too hot (nozzle and/or bed).

In my experience temperature is the most important thing to get right, print a bunch of cubes at different temps. You may find there's a range of temps that print well, for PLA choose one on the cool side.

The 2nd most important parameter is extrusion amount, although the default settings are usually really close unless something is seriously out of spec on your machine (not likely with a FFCP). Tune extrusion amount by printing a single parameter width wall and measure it with some digital calipers, tune extrusion to get it as close to 0.4mm as you can. When measuring the wall try to only measure the top layer, if you clamp down on a large section of wall cumulative error will cause you're readings to be high.

The final thing to tune is retraction, wipe and coasting settings. If you're print looks good but has a lot of stringing or "zits," than you'll need to adjust these.