The ferry terminal at Kennacraig is about 2½ hours from Glasgow; you should aim to be there 45 minutes before the boat leaves as spaces may be allocated to standby vehicles during busy periods. Ferries leave 4 times a day on weekdays and the timetable can be seen at http://www.calmac.co.uk/timetables. Note that there are different sailings on Wednesdays and the winter timetable differs from the summer. The ferry takes 2 hours to Port Askaig or 2 hours and twenty minutes to Port Ellen. You can eat on board and there are places for dogs to sit.
There is a plan twice daily from Glasgow to Islay. This is often busy, so booking in advance is advisable. See www.loganair.co.uk
Buses leave regularly from Buchannan Street Bus Station (just next to Queen Street train station) and join up with the ferries at Kennacraig. There is also a bus on Islay that connects with most ferries and will take you onwards on the Island.
There is currently a passenger ferry operating from Tayvallich at the head of Loch Sween to Jura; this runs during the summer only.
Once on Islay you may wish to hire a car; this may prove more convenient than bringing your own over. Cars can be collected from the airport, ferry terminal or almost anywhere else on the Island. See www.islaycarhire.com
Islay is an excellent place to visit on a bicycle. Among the many routes to take, it is possible to go via Arran and then cross from Lochranza to Claonaig. A short ride over the hill takes you to Kennacraig. A return (slightly more arduous) might be from Tarbet to Portavadie then over to Colintraive, across to Bute and back via Rothesay to Wemyss Bay.