assuming the mast hinges near the cabin top...
We do this all the time at our marina, although we do it after the boat is on the trailer on the tarmac. From the jib halyard where you would attach the top of the sail, attach a long line perhaps 100 feet long. Secure the other end of the halyard on the mast near the base. Have a couple of people walk the long line out in front of the boat a hundred feet or so... to the end of the line. You now have a line holding the top of the mast well forward. Have the people at the end of the line pull on the line until the forestay can be removed at the stemhead. With two or three people on top of the cabin to steady the mast, have the people at the end of the line start slowly walking back towards the boat to allow the mast to start to hinge back towards the back of the boat. People on top guide it left or right to keep in dropping on the centerline, and at a certain point are carrying most of the weight of the mast as it gets lower. You will already have made a stirrup to hold the back of the mast that attaches to either the stern pulpit or rudder gudgeons to act as a crutch for the mast when it comes down. You want to make sure it is tall enough to clear the cabin top. The people on top of the cabin, guide the mast into this mast crutch. You want this to be a slow methodical process, with the boom and sails off. Most often the shrouds can stay on. Once the mast is down, you can remove the pin at the base and slide it forward and reattach it to the bow pulpit. Secure it to the crutch as well. Collect and wrap up the stays with bungees close to the mast. Place a support for the mast between the cabin and mid mast... a old lifejacket works, and tape them together so that you don't loose the life jacket going down the highway.
This is much more difficult to do on the water as the boat must remain stationary. Theoretically you can attach a line and have a person walk forward on a dock or shoreline, but we have always opted to do it with the boat on the trailer or cradle. Once you have done it once, you can likely get away with about 4 people for the task, but the first time, you want a few more than minimum. The shrouds always seem to tangle on something when you only have the minimum number of people and there is no extra person to remove the line or shroud that is hung up.
There are a number of sites on the web that show how to rig a 'gin pole' and temporary side stays, a long line running through a block at the stemhead and back to the cockpit winches that allows the whole process to be done single handedly, but the first time, you want lots of help... and no side wind!
Good luck with your mast lowering.