If ... Then runs code when a condition is true, with ElseIf for further tests and Else for everything else. Single-line If works for one statement; block If needs End If.

Code

If total > 1000 Then
  status = "Large"
ElseIf total > 100 Then
  status = "Medium"
Else
  status = "Small"
End If

• Multi-branch

  If total > 1000 Then status = "Large" ElseIf total > 100 Then status = "Medium" Else status = "Small" End If → Three-way classification

  Order the tests from most to least specific.

• Single line

  If found Then Exit Sub → One statement, no End If

  Single-line form.

• Object check

  If Not rng Is Nothing Then rng.Select → Tests an object before using it

  The Nothing check.

• And and Or evaluate both sides, so If x > 0 And 1 / x > 2 still divides by zero when x is 0; nest the Ifs.
• Select Case reads better for many branches on one value.
• IIf(cond, a, b) is the inline version but evaluates both a and b.

• Single-line If with several statements needs colons and is hard to read.
• Comparing strings is case sensitive unless Option Compare Text is set.