Get these essential tools:
Link to ceramic screwdriver: http://www.ultibots.com/ceramic-screwdriver/
Digital Calipers (yes, harbor freight is acceptable quality for 3D printer stuff): http://www.harborfreight.com/6-in-digit … 68304.html Get the one that can do both metric and SAE - it's worth the extra $1.

I'm assuming you're on a 5/16" Z-screw so...

First, Use the calipers to accurately determine your Z-steps (ask later when you get your calipers if you're not sure how to do this).

Second, I would go to the Prusa Calculator (http://www.prusaprinters.org/calculator/) and get the "optimal layer height for your z axis".
Instead of 0.3mm use 0.2963mm
Instead of 0.2mm use 0.1976mm
Instead of 0.1mm use 0.09878mm
This is so your stepper motor can use full steps and maintain accuracy while it's not moving - do it - your layer height and overall accuracy will improve. ***Use one of these or a multiple of one of these for every Z movement in Slic3r including layer heights and any z-lift you want to use.

Third, set ALL of your extrusion widths to 1.2*nozzle_diameter, print a single walled cube (search or ask), measure the width of the wall with the calipers, and accurately set your filament diameter as follows:
((measured wall width)/(1.2*nozzle diameter))*(current filament diameter in slic3r).

Report back and we'll keep helping.

Is the pitch of the stripes the same as the pitch of the z-axis threaded rod at the back of the machine? In that case it might be z-wobble that needs a mechanical fix...

first thing I would suggest to you, if you just got this thing, is to get a multimeter and check the voltages to your motors - mine were way over powered! especially the extruder motor...

I used this guide to get mine dialed in better:
http://support.solidoodle.com/hc/en-us/ … Solidoodle

a note on this - if you dont have ceramic screwdrivers make sure you turn the printer OFF and unplug before making any adjustments to the trimpots! you dont want to fry your board! also be careful of static electricity - touching the metal frame of the printer before touching the board will help to mitigate that issue.

next up, make sure all the pulleys and belts are aligned and tensioned properly - shipping seems to be very hard on these.
http://support.solidoodle.com/hc/en-us/ … Tensioning

Then to get proper filament feed, you can follow this video's instructions (i also recommend marking an extra line at 150mms just in case - my SD4 ate 134mms of filament when asking for 100mms - completely eating the 100mm mark...)
https://www.youtube.com/watch?v=JZGdMc2ebPo

this one is also pretty good - altho a lot more technical...
https://www.youtube.com/watch?v=YUPfBJz3I6Y

Making these adjustments on mine has GREATLY improved the print quality.

Good luck!