I'm currently 6th in the Midland Trailquests Spring series and I'll be glad to give any advice I can.
The most important thing is make a map board. I did my first event with the map stuffed down the front of my jersey and wasted loads of time getting out to have a look and then stuffing it back in.
My map board is just a thin plastic chopping board cable tied on to the bars.
A watch or some other means of timing is essential. An odometer is very useful.
I've always ridden solo. Some people ride as a pair, others enter as two solos, but ride together so that if one gets a puncture, the other can carry on alone. For your first event you might as well ride as a pair for mutual support.
The procedures can vary from event to event, but normally you will get the map with the control points marked on it when you book in. Generally the harder to get to CPs will be worth more points.
You will need to have some idea of how far you can ride in the time allowed. Say, for example, you can maintain a 10km/h average, plot a 35km route on your map with a highlighter pen taking in as many high value CPs as you can.
Once the clock has started, then you get the control point values. If there's no surprises, set off on your route.
Keep an eye on the time and your average speed and be prepared to alter your route on the fly.
Use your local knowledge to your advantage. Bridleways all look pretty much the same on a map. If you know that one is a hard stone farm track and another is a muddy strip across a field, that will help in your route choice.
Where is the event ? There's a 3.5 hour MTQ event in Surrey tomorrow, so I guess it's that one.
If you look at previous results you will see there's a wide spread of scores. There's some proper fast guys (and one fast grrrl) doing the MTQ trailquests, but there's also a lot riders just out for a fun day on the bike. Don't worry about what everyone else is doing, just go out and enjoy it.