Setting dampers can be a tedious process. With dampers that have bump and rebound adjustment and, say, 30 clicks on the adjuster, 4 dampers give you 810,000 combinations!
Unless you have bought Ohlins or similar, the effect of each position of the adjuster is not likely to be the same on each unit. IE, position 10 on bump on one damper won't necessarily be the same on the other dampers due to variations in the internals. This will have to be taken into account when setting up and notes kept.
Even with identical dampers, each corner of the car will be a different weight so the first thing to do is corner weight the car before venturing onto the track. Make sure you or a person (or sack of potatoes/bag or two of ballast) of similar weight is sitting in the driver's seat during setting up.
Once out testing the golden rule is Only Adjust One Thing At A Time. You can adjust all dampers by the same amount but don't adjust bump and rebound at the same time otherwise you will get into a hell of a mess very quickly.
Wind all adjusters to their hardest setting as this is where you count the clicks from. You can't do it from full soft as this tends to vary from damper to damper. Then wind to the mid point (on your dampers that is approx 16).
If you have cheap springs, don't bother testing until they have taken a set. You can then reset ride height. Mind you, if you are serious enough to want to set your dampers you shouldn't be using cheap springs in the first place
I don't think filming the test is of much use apart from, as Stamford says, as a stop watch. You need to drive the same way on each test lap as trying to go faster by taking a corner differently breaks the OAOTAAT rule. Only once the car is set up properly can you look to improve your technique.
With regard to the actual damper settings, start with them on their middle settings, counting from full hard. Then, by halving the gap each time (Middle to full hard is 16 clicks on your dampers, so try 8. If too hard try 12, if still too soft try 4 and so on) you can greatly reduce the number of changes required to get to where you want to be.
Remember, however, OAOTAAT!
As mentioned by others, let the tyres cool down after each test so that their pressures remain constant during testing.