We recommend booking a transfer ahead of time. Canada Transfers is a great company that we've been using for years. Click here to check them out.
You can also take a taxi from the Cancun airport to Puerto Juarez where you will take the ferry. There will be many drivers outside of the airport and this can sometimes be overwhelming with everyone wanting to help you at once. Their prices can vary considerably so ask for the price before you get in the cab.
Once at Puerto Juarez, buy a ticket to Isla Mujeres on the Ultramar Ferry. There are departures from Cancun to Isla Mujeres every half-hour (on the half-hour) from 5:00AM to 9:30PM, then ferries at 10:30PM & 11:30PM. Note that most commonly, you will be sold a return ticket, so keep the portion that is returned to you for going home. Now on Isla, you'll see the taxi stand is to your left. Waiting just off of the ferry, there are also Maleteros, a friendly local with a tricycle to carry your bags. They'll lead the way with your luggage for a tip. You can ask either to go to Hotel Las Palmas or the 'Mercado Municipal' is right in front of us.
If you're keen to walk to us from the Ultramar Ferry, it is a nice 5 to 7 minute walk and will immediately immerse you into our beautiful island. Walk across the raised crosswalk (that goes between the Señor Frog's store and the 7/11) and continue down that street. It will open into the Zocalo (town square) On your left there will be 'the Express' this is the main grocery store. Turn left down that street after the grocery store (the hospital will be on your right). We are about three blocks down, on this street (Guerrero) on the left hand side. You should be able to see our sign from about a block back and we're a yellow building. If you do happen to take a wrong turn along the way, ask anyone where the 'Mercado Municipal' is and we're right across from there.
Hint: A Maletero, as described above, is the best of both worlds. You get to immediately enjoy and familiarize yourself with the island while they lead you to our hotel and handle your luggage!