Here are a few pics and notes from my training at 5k feet. I can provide my basic single player mission (5k airstart, shop targets) if required.
1. Cockpit
Note that I am trimmed to level flight and the slipball indicates that I am slightly crabbing. This is compensation for lack of aileron trim. I wouldn't recommend this for the trip out but when closing on the target I find that the reduced roll is worth the loss of airspeed.
I have found that the Blenheim altimeter is often set 200-300 feet too high. I click it left three times so am ~300 feet lower on instruments than default settings. This can be easily verified - just try to fly to 100 feet and you will find that you are a submarine! Not sure about other aircraft.
2. Bombardier dash
These instruments are your friends! Pay at least as much attention to them as you do to your target. Constantly update your speed and altitude settings into the sight (see below).
3. Bombardier view
The view from the pilot's seat is rubbish so it's worth transferring here after you are roughly trimmed and closing on target. I find it useful to adjust the screen view down a bit to provide a closer horizontal reference for the horizon from the monitor edge. I wish they had put an artificial horizon in here...
I find it best to be turning slightly right into your target since visibility is much better on this side.
4. Bombsight breakdown
Note that this is the view when you have 'leaned to gunsight' (or whatever the command is). This is critical (see my post above...)
#1: Altitude adjustment in 100s of feet. Strongly recommend binding keys to this.
#2: Target should run down between the strings. My target is moving left so I am compensating. I could just as easily adjusted the sight 0.5 degrees to the left.
#3: Targeting reticule.
#4: Velocity adjustment. Also highly recommended for a key binding. I use the number pad for my sight adjustments.
It is worth noting that I get best results when I do not follow protocol. First, I underestimate rather than overestimate my altidude (e.g. if at 5050 feet I will enter 5000 instead of 5100). Second, I do not adjust to TAS but rather input the IAS. Adjusting for TAS makes me land short.
Edit: I am getting best results when trimming the Blenheim for proper hands off flight (as in go and make a cup of tea and it's still fine a minute or two later) which means I am side-slipping at about +1.0 degrees. I then adjust the sight to -1.0 degrees which compensates for the motion and keeps the target lined up in the rails until release.)
5. Release point
Don't forget to open the bomb bay which is another essential key bind. Continue releasing until all bombs are away. I get rid of all bombs across the target length.
6. Target perspective at release. The distance is 2.04 km.
7. Impact. There were no direct hits but there evidently didn't need to be!
This is not particularly easy, at least for me. After a few hours practice I have a good feel for the sight and am getting pretty close to my targets. If you are aiming for an airfield or similarly large target you should be hitting it from the start.
I also find it easier not to use freetrack for this but rather just drag the view with the middle mouse button as necessary. Stable view and slow corrections are what this is all about.
I have not addressed getting up into the air since this is covered by ATAG_Dutch videos above. My loadout is 4x250lb with a #42 pistol, 0 second trigger. I use an 11 sec trigger for skip bombing.