Well, you have some advice to sieve through here! Technically, Thomas covers a great many things that you should consider, but if you are like me and have limited time juggling family life, a professional career and a few other interests, then you would want to take a few short cuts with the least risk of losing something important. So think about the following:
Change one thing at a time, until you are sure you understand how that affects you. The most important things are (in my view): Choice of developer and dilution; agitation (do not underestimate this!); developing time; temperature; exposure (including any bias/fault on your camera or lightmeter). If you add filtration, that will change a few things, especially how skin and sky are rendered. If you do not have a densitometer, and cannot make darkroom prints, it will be quite difficult to benchmark. So if you could maybe borrow a densitometer, or mail your test negs to somebody who can print or measure them for you, that would help.
The following is an easy (but tedious) way to get to more or less understand the materials you are working with. You want to know how to expose and develop while being able to maintain detail in both the shadows and highlights into the zones that are important to you. The technique I use comes from John Blakemore's Black and White Photography Workshop. You have to take something like a single-tone towel or coarse fabric - something that has texture. Flat and smooth objects like white walls and paper do not give you any means to gauge whether detail is visible or not. Colour patterns won't help either. So you take your towel, and using the zone system designation, photograph it at zones 0 through X. Develop and print (or scan) for zone V, then print all frames at the same exposure, and assess where you are in terms of visible detail. That will then give you an indication of how to expose. You could force the contrast up or down by changing the developing time, but only if you know what you are doing, and having exhausted your tests at the standard developing time. You will do this once for every film/developer combination, which is why almost all the experienced guys advocate sticking to as few as possible. Three films and three different developers already give you 9 tests to run. It grows exponentially if you have more. It might surprise you, but after having done this with FP4+, HP5+, Acros and TMax 400, I am back to exposing at box speed and developing at standard times with Rodinal 1:50, with agitation once a minute as two gentle inversions. This gives me more than enough in the negatives to work with in terms of dynamic range, and the negatives have punch and accutance when printed close to Grade 2, assuming average lighting and subject contrast. There is one important caveat: I expose for a zone, rather than averaging with the camera lightmeter. That is usually zone IV, the "high shadows", sometimes zone III. I almost never bother about the highlights, but if the contrast is high and the highlights are very important, I might meter them and reduce the developing time. Since I shoot roll film, that is the exception and not the rule. BTW, you are lost without a spot meter, either in camera or handheld.
Since there is an aversion to zeroes and ones on this forum, I will not delve into your scanning methodology. Suffice it to say that some scanners (and/or software) fare less well with black and white negatives than others. You might want to solicit advice in the appropriate forum on that topic. It took me a while to figure it out, and I am still not nearly as happy with scans than with my darkroom prints from the same negative. The upshot of this is that it motivates me to make darkroom prints, since I absolutely want to see what the negatives are capable of.
EDIT: Drew makes it sound as if it is easy to use printing techniques to salvage a negative. While experienced printers make it look easy, in reality it is not so simple. At the very least, it is time consuming. There are some scenes that are nigh impossible to expose optimally for the entire dynamic range, and then such techniques are very useful to get a quality print. But they are for most of us the exception and not the rule. You should not expose and develop your film in such a way that special techniques are required for every subject. Then you are definitely doing something wrong.
