How do you precipitate an ion completely from a solution?

Answer 1

You cant.
The key word here being "completely".

No matter how insoluble a given precipitate is, it is always soluble to some, very minor, degree.

However, by choosing to precipitate a compound with a very low, practically zero, solubility, the ion is (for all intensive purposes) removed from solution.
When dealing with such low-low solubilities, the Ksp value for the compound becomes important...the lower the Ksp, the lower the solubility.

Answer 2

by adding a solution containing an ion that it forms a precipitate it for instance if youwere trying to precipitate chlorine from NaCl you would add maybe AgSO4 so silver chloride will precipitate

Answer 3

to get it completely out, you have to remove the precipitate from the solution before trying to percipitate more out of it. Use a filter crucibule to do it. wash it with a nutrual solution (one that will not cause the percipitate to dissolve, nor one that will cause other ions to percipitate out)
you know when you have gotten all the ion out of the solution when you are able to add the solution that causes it to percipate out with out seeing anymore cloudyness.