I have noticed that "Cleared to land" is often issued by tower when the previous landing aircraft has yet to vacate or I am number two.
You are number one. The other aircraft has already landed. Or your separation is such that you are able to complete the approach and land after the other aircraft is down and clear. "Cleared to land" meas exactly what it appears to mean. You're cleared to land. Nothing more, nothing less.
Would I be correct in saying that it means "Cleared to make your approach" and landing is up to you when the runway is clear?
No. "Cleared to land," means cleared to land. Not cleared for approach, but just what it sounds like it says: "Cleared to land." You always have the final responsibility to determine if a clearance is safe. There are no exceptions.
Part of every briefing when I know I have traffic ahead of me or on the runway, including released to takeoff, is a reminder to be prepared for a missed approach.
You may be cleared to land, and subsequently an aircraft cleared to takeoff from the same runway before your arrival. You'll be told this when you're given your landing clearance.
From the FAA ATC Pilot/Controller Glossary:
CLEARED TO LAND - ATC authorization for an aircraft to land. It is predicated on known traffic and known physical airport conditions.