If you find you use a lot of semi-colons, there’s a good chance your sentences are too long. Break things into smaller units, especially for readers using a small screen.
Semi-colons can be useful in lists where the enumerated items are clauses with internal commas, so you know what goes with what. Parentheses could help, but a thicket of round brackets (or any kind of brackets, really) is hard on the eye (as my friend and colleague Angela Swan points out).
In those situations, it might be easier for your reader to put the items in a bulleted or numbered list. In my view, you can dispense with the semi-colon at the end of each line.
Do not place a semi-colon in the salutation of a letter: Dear Ms Ali; is just weird. A colon or comma would do. Or you can dispense with punctuation altogether; the white space after the salutation provides an adequate break.
Note the use of a semi-colon in the previous sentence, where it effectively joins a thought that explains a previous one. A comma after altogether would be wrong, as you’d end up with a non-grammatical comma splice or run-on sentence.
A dash could also be used in that sentence – and would add a bit more emphasis.
But go easy on dashes. Too many and they lose their punch.