Just wandering, how to make those lines to be close one to another? What configuration parameters to change. I am using Prusa i3 MK3.
It’s based on the thickness of your layers. The thicker the layer, the closer the lines are, but the lower the detail.
@Xenomorpheus I set the layer thickness to 0.1 mm but the base layer thickness is forced to be 2 mm.
ah, that’s for better adhesion. If the base layers aren’t thick enough, they don’t adhere well to the surface.
Given that this is your first layer, you generally want to have a little squish. There are a couple of things that can affect that. The first thing to consider is to set the layer thinkness for your first layer to be slightly larger than other layers. Second, check your nozzle height. You may need to lower it towards the bed slightly (say 0.05mm or so). Lowering will add some squish, joining the lines.
@Xenomorpheus Thanks. That make sense. Can this be solved with over-extrusion settings?
@Farzad_Battiwalla Thanks. I’ll try that.
And while I was ok with the first layer, the printer started to behave. For some reason it shifted layer horizontally. Any idea what could cause that?
missing/deleted image from Google+
Shifts are either bad adhesion, poor calibration, or temperature differences . . . usually.
@Xenomorpheus Well, adhesion is very good - no shifting of the model. It seems that printer decided to move its head by 3cm to the left.
Presuming the print didn’t slip on the surface, the printer shifted where it was printing. The two most likely causes are the toothed pulley being loose on the stepper motor shaft (especially if the shaft is not D-profile but is round) and missing steps from not setting current correctly for stepper driver for that axis. I had round-shaft stepper motors and fixed that with a touch of dremel to give the grub screw in the pulley somewhere to bite. Don’t adjust stepper motor current blindly; follow instructions to not start a fire. 
@mcdanlj Interresting. Thanks, I’ll investigate this, but the shift is very consistent on this specific model. Other models were printed perfectly fine.
There could be an error with the slicer or that stl file is corrupted somehow. I’d also check the orientation of the print, sometimes there’s something going on that can be missed.
@Xenomorpheus Thanks I’ll try to reorient print by 90°C 
@Lukas_Mathis I built it from the kit. Tested the tension - no movement or slipping steps. The first layer is .2 mm as per slicer default settings. Will do calibration again. But I got a strong feeling that this is as software glitch somewhere.
If you’re suspecting the model, it’s a good idea to use a gcode viewer to double check the generated gcode before sending it to the printer. If there is indeed a layer shift in slicing, you should see it when you move to the respective layer. The one I personally use is http://gcode.ws/#. I highly recommend it.
@Farzad_Battiwalla Hmm, nothing terribly wrong with the gcode. I am realigning printer. Also asked this in Prusa forum
It might be a slightly clogged nozzle which limits the amount of extruded material, which has happened to me before.
A friend who has the MK3 mentioned that the printer can tell you if your belt tension is within acceptable range (if it’s too loose it will cause layer shifts). In your second pic it doesn’t look like the part came off the bed and the MK3 has skip detection so that really only leaves belt tension. When you pluck the belts it should sound similar to the deepest string on a guitar.
As for the first layer lines, from the second pic you posted it looks like the the 2nd layer also has gaps between the solid infill lines which means its most likely not first layer thickness and it is very likely to be improper extrusion that’s causing the issue. Check to make sure your filament is actually 1.75 mm wide (+/- 0.05 mm), your slicer is set to 1.75 mm filament, and your nozzle diameter is correct in the slicer (0.4 mm comes stock on the MK3). If all that looks good go ahead and calibrate your extruder (guide: https://www.youtube.com/watch?v=YUPfBJz3I6Y&vl=en).
If you still have issues after this please post a new picture so I can continue to help. There is a chance your nozzle has a partial clog, my friend with a MK3 also had inconsistent extrusion due to a partial jam. We were able to clear it out by feeding some ABS at high temps (250-260 C). Cold pulls with PLA wouldn’t work, I suspect they were testing the hotends with ABS and there was some left in the hotend that wouldn’t extrude with the PLA.
I agree with the partial clogging suspicion. It has happened to me precisely due to switching from ABS to PLA. Leftover ABS (or any other high-temperature material) will not soften enough at PLA temperatures to be pushed out.