With flights to Paris from all the major airports across the UK (and some of the smaller ones too) you won't have to travel far to catch your plane. Eurostar offer train travel direct to Paris from London through the Channel Tunnel and you can take your car across to France the same route from Folkestone to Calais. Or if you prefer a bit of the open sea, ferries run from Dover to Calais where you can then make your own way to Paris. Eurolines also offers low-cost coach travel to Paris from stops across the UK.
Paris Airports website
If you have arrived by train or by plane there are a variety of options for onward travel to your destination. It's easy to get into central Paris from either Charles de Gaulle Airport or Orly Airport as they are both on RER lines, the suburban railway, which connects with the metro, or both airports offer shuttle buses to the centre as well. If you arrive by train in to Gare du Nord it's similarly easy to get onto the metro, and there are plenty of buses too. Taxis are quite expensive in the daytime, particularly if they get stuck in traffic!
The best way to get around Paris is on foot as most of the major sights are easily within walking distance and you get to enjoy the quaint streets on the way. You could also hire a bicycle for short trips with the city-wide Velib cycle scheme. For faster trips around Paris, or to travel further afield, the metro is brilliant, as well as cheap. There is also a good bus network which uses the same ticketing as the metro and may be a better option if your metro journey includes lots of line transfers. Night buses run around the city after midnight and once the traffic dies down taxis are an economical way to get home in the evening.
France has an excellent road network if you want to hire a car or drive your own, although most of the major motorways do have tolls. Internal flights are a quick way to get from one part of the country to another if you're short on time, but you can see a little more if you travel by train. The trains in France are comprehensive and this makes it very easy to get around, and with high speed rail the long distances will fly by.