When sailing offshore or, for that matter, any time when you know from the weather forecast that the wind may strengthen considerably, you must, I repeat MUST, run all your reefing lines.
If your mainsail has two reefs but you only have one reefing line, make sure you run a light line as a ‘mouse’ to the second reefing point in the leech. If/when you need to take in a second reef, you can then tie your reefing line securely to the mouse and gently pull it, drawing the reefing line up through the reefing point and back down to the boom.
Using a mouse is OK but it is preferable to have reefing lines available for all the reefs you can take in your mainsail.
If you don’t rig your boat so that you’re ready for the increased wind strength, when the time comes to take that second reef, conditions will be far too dangerous to allow one of your crew to try to lead the reefing line.
In Boat Handling I and II, I discuss how to reef a mainsail in detail.