I recommend rating the film at half the published rating, for starters (e.g. HP5 (published iso: 400), rate at 200). Determining correct development time can be done this way:(posted 8509 days ago)Point two light bulbs at a white wall -- some texture preferable -- (45 degrees to about refections), and shoot the wall, placing it in a zone VII.
If using roll film, cut the film into three sections. Develop one section at your projected "n" developemnt time.
Then print this negative test strip style (2 1/2 grade filter), with two second intervals, being sure to print some of the clear film base, along with the zone VII (wall) image area. The interval at which the clear film base turns black indicates the minimum print time. What does the zone VII wall look like here? If it prints a zone VII, then you have the correct development time. If its a zone VI, you've underdeveloped, if VIII, over developed.
If its off, repeat with the other pieces of film. If you got a zone VIII, reduce developemnt by 20% (generally 20% per zone), or increase, if its a zone VI. This will then be your corrected "N" Be sure to keep dilutions, agitations and temps constant.
For film speed, photograph a well textured, uniformly lit subject, and place this in zone III. Develop the film at your newly determined N development time. Once again, determine the minimum print time (as above). If, at the exposure where your film base goes black, you get a nice zone III (good texture, but almost black), then you've got the correct film speed. If the image area is a zone II or less, then you need to rate the film lower (maybe one stop ~ 100 ISO for my HP5 example). If you get a zone IV (the "blacks" are muddy), rate the film one zone higher 300 ISO for my HP5 example).
Good luck and have fun!