There are a few cura settings to get around people who have trouble levelling. One of them is called "raft". The alternative is having the first layer be .3mm thick (you can have the first layer be thicker than the remaining.
Having said that here's my homing procedure if you want to do it PERFECT:
First heat up the head to 180C and when it is warmed up remove the filament. Then clean the filament off the head with a tissue. Don't burn your fingers.
Now to the Z axis homing only if you can e.g. proterface or UC controller. If you really must do X and Y also then you have to wait until the XY axes are turned off or turn them off with UC.
Now by hand move the head around and move it as close as possible to each screw. Use an ordinary piece of paper. I typically use a sticky note with the sticky edge near my fingers. This kind of paper is about .1mm thick. Typical printing paper is okay also. Slide the paper under the head and tighten the screws until the paper has zero friction, then raise the bed at that spot until there is an increase but not so much that the paper gets stuck or can't be inserted under the nozzle. Now repeat 3 times for each screw. Then repeat the whole thing again (again with a hot nozzle as a hot nozzle expands a little and you want to calibrate/level while hot.
Repeat going around all the screws many times. You might have to do it 5 or 10 times as when you adjust one screw it might mess up the others.
Once it seems really good then I usually just stop there if .2mm layers. If .1mm layers then I loosen each screw 1/8 turn to account for the paper thickness of about .1mm.
Having said all that your metal rods might be warped or your bed might not be flat. Some people grab the z axis and twist it WHILE PRINTING! To get the skirt good. On rare occasions when I mess up the leveling I get lazy and push down on the bed (if that's what is needed) to get the plastic to come out (sometimes I mess up and the head is touching the bed and pressure is building up and nothing is coming out). By the second layer I usually don't have to do anything.
Cura has a bed leveling wizzard. Besides that you could just adjust up your front screws 1/8 turn at a time and testing in between with a big print like your iphone. If it fails on first layer stop the print and adjust another 1/8 turn. When it looks right let it finish the print.
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