Getting to the ground
It's pretty easy to get from Kings Cross to Brentford, from where it's only five minute walk to the ground. The best way of doing it is to catch a tube to Vauxhall and then an overground train (every 15 minutes). The total journey time is 50 minutes if you hit it right at Vauxhall. The cheapest way is with an Oyster Card or contactless debit/credit card (£9.50 in total). Otherwise you'll need a One Day Travelcard zones 1-4 (£12.10). If you happen to be driving there then you should expect to have to park a long way from the ground as virtually everywhere around the ground is residents parking only. Your best bet is probably the streets off Enfield Road and junction road, north of the M4. This is also residents parking, but only up to 4pm as far as I'm aware.
Griffin Park is famous for having a pub on (more or less) each corner of the ground. One of them is closed at the moment though, and the Princess Royal appears to be no-go for away fans. The Griffin is the closest of the four to the away end, but it's the New Inn that tends to be the most popular with away fans, and I'm pretty sure that's where I was the last time we played at Brentford. On or just off the High Street, around a 10 minute walk from the ground, are the highly rated Brewery Tap and Magpie and Crown, with the latter normally getting a mix of home and away fans. North of the M4, and so convenient if you're parked somewhere around there, are the Globe and Lord Nelson, the former in particularly receiving good reviews.
Kings Cross pub map
Football Ground Guide