To get to Paisley, there are multiple options:
If you are coming from Glasgow, take the M8 westbound and take exit 27. If you are coming from Greenock, take the A8 eastbound. Paisley is just west of Glasgow Airport, which can be reached via junction 28 of the M8.
If you are coming from Glasgow, take the train from either Glasgow Central or Queen Street stations to Paisley Gilmour Street. If you are coming from Ayrshire, take the train from Irvine to Paisley Gilmour Street. There is also a direct train from Edinburgh Waverley to Paisley Gilmour Street.
If you are visiting Loch Lomond, take the A82 southbound and then follow signs for the M8 westbound. If you are visiting the Clyde Muirshiel Regional Park, take the A760 and then the A737. If you are visiting Glasgow Airport, follow signs for the M8 and take junction 28.
The closest airport to Paisley is Glasgow International Airport, which is only about 2 miles away. The best route to take from the airport to town would be via the M8 motorway. It's a quick and easy drive that should take no more than 10-15 minutes depending on traffic. There are also plenty of taxis and shuttle buses available at the airport if you prefer not to drive.