The visit visa process is generally straightforward, you complete an application on the UK Border Agency website, arrange an appointment at VFS Manila to submit the documents and biometrics, and take some photos.
The cavite being, as is mentioned above, the EVIDENCE! You need to provide a letter of support detailing the plans for the trip, itinerary and your relationship with your girlfriend.
You need to prove two very major points; 1) That your girlfriend has a compelling reason NOT to remain in the UK at the end of the trip, i.e. she a letter from her employer, assets in the Phils etc and 2) That sufficient funds are available to cover the trip, with full proof of these funds.
With these documents in hand, it should be very straightforward.
Good luck.
