FM Antenna. Any tips

Finding a fitter that know what they are doing is probably the biggest obstacle. Not many fit FM Aerials (apart from the crappy little omnidirectional things) these days. 

1 - Find a decent fitter (your dealer should be able to recommend a good one)

2 - They'll size the antenna based on distance from the transmitter and any other local considerations. A 4-5 element antenna is usually more than enough. Ron Smith Galaxy antennas are the Rolls Royce of the FM antenna world but are big in size and need a decent mast and brackets too.    

3 - Use quality double screened coax - WF/CT100 ('satellite' cable) is good and readily available. 

4 - Try and ensure an unbroken run of cable from Aerial to Tuner. 

All that wot james sez.     Maybe a Ron Smith is a bit OTT considering your location,  but listen to me !!  I've got a Ron Smith & I'm only 3.5 miles from my local 45kW transmitter.      Assuming you're still in the Sarfend area,  your FM transmitter is Wrotham over the water in Kent & aprx 21 miles away,   It's pushing out 125kW & a 3 element aerial will be the best choice for NAT-05,  but a 5 element if you go for a NAT-01.    Good makes are Blakes & Antiference,  plus of course the Ron Smith monsters, 

Thanks guys. There's a transmitter at South Benfleet which would be closer. Wouldn't that be my best bet?

South Benfleet is a local low power FM transmitter that has only  BBC Essex on 95.3MHz &  Heart FM on 96.3MHz.    Wrotham has all the national stuff & is one of the most powerful TX's in UK,  enough power to cover out to Bucks & Berks on the other side of London. With a 3 element pointing straight at Wrotham, South Benfleet is aprx 90 degrees off beam but is close enough to you to pick up OK.   

I used to use Wrotham when i had my NAT-02 and we're close to the edge of the coverage area to the west of the transmitter map. As Mike says, with your location you'll have no issues using that transmitter. 

Excellent. Thanks guys.

Spend a while looking at the AerialsandTV.com website - loads of information including transmitter data and if you are any good at DIY you may well find you can save money. I know high grade outside aerials are best but I found I could get a full strength signal quite easily on FM from an aerial in the loft.