What temp are you using? If its the silver PLA from Prusa, around 205 works well for me. Its a very forgiving filament.
Steps to calibrate and check:
Are you using bed temp calibration? - I prefer not but I have my start GCode for every print make sure PINDA is away from bed while it heats up, and then calibrates.
Make sure bed is cooled before starting new print/calibration
Start on the lower end and slowly adjust Z until it looks smooth. Once its done printing, check for holes between infill and perimeter, if so, increase infill by about 20 until they disappear and you have a nice smooth finish.
Make sure the extruder hobby is tightened and the securing bolt is on the flat side of the motor driver.
Calibrate your extruder first (Search Forum)