What is the difference between presenting myself well and lying on a resume?

Presenting yourself well means choosing and wording true information to show your strengths. Lying means stating something that is not true or creating a false impression. The line is about facts, not style.

Fine:

• Choosing your best achievements and leaving out minor ones.
• Using strong, accurate verbs and the employer's terms.
• Describing your real responsibilities clearly, even ones beyond your job description.

Not fine:

• Changing job titles, dates, employers or qualifications.
• Claiming skills, tools or certifications you do not have.
• Taking credit for results you did not contribute to.
• Inventing or inflating numbers.

A practical test: would your former manager agree with every line, and could you explain each one in detail in an interview? If the answer is yes, you are presenting yourself well. If you feel the need to hope nobody checks, it has crossed the line.