Since I pretty much do not tune anymore, here's some info on how to scale aftermarket injectors, when you have no datasheet for them.

Let's say you have injectors on the car for which you do not have any clue what the TVUB could be, maybe you're not 100% on the flow rate either.
Let's assume for the moment that everything else on the car is linearized - because if not, then good luck to you. It is still doable, but without a huge amount of experience and knowledge you will not find out what's scaled wrong, so it is outside the scope of this topic.
Also before starting, pressure test the car and make sure there are no air leaks whatsoever anywhere, otherwise you're gonna have to do this all over again after fixing the leaks.

1. Set FKKVS to 1 everywhere.
2. Set KRKTE into the ballpark that you think it could be. By far the easiest way is to divide the OEM injector size by the current injector size and multiply KRKTE by this number, instead of trying to do theoretical calculations.
3. Take TVUB from some random injectors, that are at least the same type - e.g. EV6, EV14.
4. Start the car, if it doesn't start, you probably messed up really badly, so try to correct your error (or remove and clean the sparkplugs if you totally flooded it).
5. Let it warm up fully, so it's completely hot and there is no load on it.
6. Find KRKTE value so that you have more or less 1-2% fuel trim on idle with the hot engine.
7. Put some load on the engine, e.g. turn on the aircon, rotate the power steering, slip the clutch a little, put it in D if it's an auto instead of P/N, whatever. Observe what happens.
a) If the fuel trim goes positive, increase KRKTE, decrease TVUB at the voltage where you are testing (or just multiply the whole table), so FT is still good on idle, but does not drift away on load.
b) If the fuel trim goes negative, decrease KRKTE, increase TVUB at the voltage where you are testing (or just multiply the whole table), so FT is still good on idle, but does not drift away on load.
Usually it is good to change TVUB in 2% increments. Repeat this process until it's more or less stable, then proceed to 8.
8. Set the car on idle, fully warmed up. Increase the RPM, to 3000, then 6000 rpm without any load on the engine.
a) If the fuel trim goes positive, increase TVUB, decrease KRKTE to compensate, so that you still have good fuel trim on idle.
b) If the fuel trim goes negative, decrease TVUB, increase KRKTE to compensate, so that you still have good fuel trim on idle.
Repeat this process until you can slowly increase the RPM on hot idle and the fuel trim doesn't drift away.

And you're pretty much done. The rest compensate using FKKVS. Beware of large changes (more than 5% on high RPM), this most likely means your fuel pressure is dropping -> verify with a fuel pressure gauge.
Make sure you do not make any sudden movements/load changes, as your tip-in/tip-out enrichment might not be correct - those can be adjusted via KFBAKL/KFVAKL by making sharp throttle movements and observing what actual lambda is doing, but only after you have set KRKTE and TVUB correctly.

Thanks prj, excellent summary. I should add it to the wiki.

Completely irrelevant if the car has been running until warmup, the fuel will be evenly mixed on any fuel system with a return.

I'm like a week too late to the party, maybe this is useful to someone.. Thanks prj!
http://nefariousmotorsports.com/forum/index.php?topic=320.msg151363#msg151363

Total fuel trim. Disable LTFT if it's easier.

No, it is not the opposite at all.
Understanding how the hardware works helps to avoid asking such questions.

The last step is fine tuning. Read the whole post.

Except it is not "the opposite".
If you knew the hardware, you would understand that point 8 is the final step, needs to be done only once and has a very small effect.
The reason it is there, is to account for non-linearity of injectors, and due to the fact that the engine behaves differently in different airflow situations. To make sure you do not bake that non-linearity into TVUB, where the non-linearity should be handled by FKKVS.

But hey, you can do it however you like.

Just keep in mind, that there is more than a decade of actual experience between every word and letter written here.
Something you seem to lack.

It needs to be done exactly in that order, period. If you do it in reverse order or you do one step, but not the other, you will never have a good result.
The input to the first part is increasing load at a fixed engine speed in a low airflow situation, the input to the second part is with much higher airflow but lower load. The engine behaves completely different with more airflow.
Two completely different inputs. The fact that the adjustment is worded one or the other way makes no difference. You are tuning the same two parameters. Your assumption that somehow 7 and 8 cancel each other out is BS, which shows your complete lack of understanding.

7 gets the rough KRKTE and TVUB parameters, 8 gets the correct/precise KRKTE and TVUB parameters from that. You can try to do only 8, but good luck to you. You better know all the math in your head eyes closed, and the engine better not have the tiniest air leak.

No, it does not mean anything. This is not how you check for correct MAF scaling. Both can be wrong.
No.

Yes it's wrong.

MAF affects load. Having incorrect MAF calibration means that everything in the engine from throttle and knock control to ignition is wrong.
Your approach of garbage in, garbage out makes tuning and getting anything right a nightmare.

This is a perfect example of how not to tune.