Map reading is an ability that needs practice, skill and application to develop. Getting it right will lead to you to a nirvana of completed patrols, dry feet, happy blokes and bang on timings. Getting it wrong will lead to missed timings, pissed of blokes and universal slagging.
It should be noted that those who slag loudest are usually the ones without the map. This is in itself interesting.
There are several salient lessons that will help you find your way and more importantly some top tips that really help.
Feel free to add lessons / tips below.
Plan your route carefully and don't trust yourself. If you need to go from A to B what route are you going to follow and how are you going to know if you are on it or not? What are the conditions like when you'll be on route, a straightforward route in the day may be very challenging at night in the rain. It may be bright now but by the end of your patrol it might be dark, is the last bit of the patrol tricky and how will you do it in the dark? If you do your thinking now with that cup of tea it will save you trying to make it up on the spot with your head in bush with a pin hole torch and all the blokes in fire positions....
Think of your route as a collection of short hops (legs) from one feature (that you can identify) to the next. Think of a corner of forestry block, road junction, bridge over stream, farmhouse, power line. These are often called "way marks". If patrolling, choose a number of these waymarks as your RVs. These should be obvious features (if you are in BATUS - unlucky) that you / the blokes can recognise.
Connecting these features should be something you can follow, see or recognise / you can also think of things that will tell you you are NOT on route. Paths are good but can also be deceiving ( and deadly if they are ambushed / mined ) also tanks make new tracks everywhere they go, forestry roads are notorious for appearing and disappearing at will, fence lines are often marked on 1:25,000 maps and are hard to miss, valleys and ridges provide easy features to walk on/through. Connect your way marks together by the features you will follow.
TIP If you are aiming for a particular spot on a 'crossing feature' e.g. a fence line, stream etc. then set your bearing a little off to one side or the other deliberately. When you hit the feature you will then know definitely whether to turn right or left.
Corner of forestry block via fence line to road, turn left on road and follow - road junction.
TOP TIP: You cannot go wrong if you write a route card prior to the patrol. It will save you taking bearings and checking grid references every 5 minutes, and should contain a short description of all legs. Using the route card will make your patrol a whole lot easier, however remember you DO still need to check your map!
If you feel super special and happen to have one around ...try writing your route card on a stiff talc (transparency) in waterfast ink. You can now backlight your route card using ambient light so you don't need to get your torch out! This will make you feel very special indeed and is a step down the road to buying yourself the biggest diving watch you can find.
Knowing how far you have gone and how far you have yet to go is really important.
Corner of forestry block, via fence line to road (550m), turn left on road and follow (750m) - road junction.
If you think you will reach a feature like the road from the forestry block via the fence line in 550m, and 900m later you haven't found the road, that should tell you that something is wrong.
You need a good way to measure your distance travelled
If you are in a vehicle you have the odometer and the driver can reset the trip and tell you exactly how far you have gone. If on foot you have some options.
If you know how fast you are moving and know how long you have been walking you know how far you have gone. Time is added for uphill sections and you need to think about the ground (time over good paths non tactical in the daytime in patrol order will be a bit faster than cross country, across baby's heads, tactical in the rain at night with no moon carrying a small sofa on your back with two drill LAWs and the D10.)
A good guide is 5km an hour easy pace, moderate load in the day non tactical, with 10 mins added for every 100m of ascent. Time should be added for conditions (load, weather, situation etc) north of this estimate.
If you know how long your stride is and you know how many steps you have taken then you know how far you have travelled. This is a really good trick and you need to try it. Measure 100m and walk across it fully loaded and in patrol order. Count how many paces it takes you to cross that distance. Do it five times and take the average. (I count double steps i.e. every time my right foot strikes down so I only count half as often). Now when it gets tricky (if I don't make the fence in 500M I've fecked it) count out the paces and reset every one hundred metres.
Counting gets confusing so there are some tricks:
Little ones, dumb-arse, in your pocket and move one to the other pocket at 100m.
The compass needle will (should!) always point North (provided you keep it level and don't stand next to a tank). In order to find out which direction you are travelling / wish to travel, turn the bezel (thats the bit with the numbers on it) to the bearing required. Now, turn your whole body until the red needle lies exactly within the red arrow drawn on the base plate. The luminous indicator will now show the direction you need to travel.
To take a bearing from the map, lie the compass edge along the following:
Bottom corner of compass on your current location. Edge of compass should pass through your destination.
By turning the bezel until the grid lines match up with the lines on the bezel, your compass will be set on the map bearing. Don't forget to add the Grid Magnetic Angle!!
More on the history of the compass here
For more information and the history of Celestial Navigation (any object in the sky), start with this wiki page.