To me- the key to length gaining is in a few steps:
1- As a start of EVERY length session it is an absolute MUST to perform the DLD Blasters Principle. You can skip the stretch (which is good, I recommend it), but what is SO important about this phase to me is that I exhaust my PC and therefore have nothing to resist the stretch. We all tend to do "defensive" kegels here and there. With this- there would be nothing to hold it. If you are not into this principle or can not do RKs (since we call all do kegels I think, it is only the RKs that are a problem for most brothers)- then jacking off before a length session would be the best. It perfectly mimics the blasters bringing exhaustion. Another way to do this is with meditation concentration. This might sound a bit awkward, but it is true- just completely relax and conciously try NOT to kegel. (for these 3 I mention in this point- if any of you want- I can link the threads I have read that so you can find more information on how to- step by step. 2 of the above mentioned have been written by DLD himself and the 3rd one by the almigth German Stallion!)
Exhaustion- Once you get to the point of exhaustion- just ride the wave and let it grow longer and longer. Whether it be ligamens, tunica or whatever- exhaustion is the way to go! There are quite some methods to reach this, but what I believe is the best way is to increase time and keep tension normal. Now, I am NOT saying that big intensity is bad!!!!! I am saying that to me- a longer length session exceeds a more intense one. Whether you hang (which is one of the BEST ways to gain), extend or do manuals- I believe this is the way.
For everyone that is interested- I can write a more broad post mentioning more things and giving additional explanation backed up with evidence and experience. But now- I am just too lazy to do it and don't know whether you'd be interested rofl!