Early on in my film photography days I sent everything to a local lab to develop and scan. It was confusing at times to get the images back and they'd be grainy, or the colors off - it was impossible for me to figure out what went wrong (largely because I didn't keep great notes on the shooting conditions and camera settings!). At some point I bought a film scanner and THEN things started to click. I had one image in particular that I remember shooting in bright sunlight, and I had stopped the lens down to f/22 because I was using very fast (1600 speed) film. The image was not only nearly impossible to see, but very clearly right-shifted on the histogram, meaning overexposed. That was how I discovered that my aperture setting wasn't working! But I had finally made a connection between negative quality and image appearance. Soon after that I became more interested in developing my own film - quite simply it was an economic decision because the cost of chemicals (after the initial investment in equipment) was going to be cheaper than the price of the lab, but I was also hoping it would be faster and give me more control over the process.
At this point it's worth diverting to talk about how film photography works - as I discussed in my earlier post on pushing film, there is a two-step process where the light causes an initial chemical reaction on the film emulsion, and then a second reaction occurs (in fact, several) during the development process to create the film grains on the emulsion and then remove the unexposed/developed emulsion. This is why they're called "negatives", because the light-exposed areas actually look dark on the film strip and the dark areas of the image (which are less exposed) are removed, leaving the film strip see-through. Faster (higher ISO) film emulsions will generally have larger grains, to increase the sensitivity, or a different mix of chemicals on the strip. Slower films will generally be finer-grained - this is very similar to high-ISO settings on a digital camera introducing digital noise to the image.
It's therefore obvious that there is an inherent problem with developing film - how do you get the film OUT of the canister and exposed to developer without exposing it to light? The obvious answer is a darkroom, but I don't have one and thankfully neither you don't need one either! What you probably will need is a film changing bag, but that step is tricky. You'll need decent developing reels (the ones with the wider flanges are best by far I've found) and you should practice in daylight with a spare roll before you move onto the bag/darkroom. Most film developing tanks will come with reels, so look closely and read the reviews to find the best fit for you. Some folks prefer metal reels, I've had no issues with plastic so long as they're dry.
Once you have the negatives safely in the tank, the actual developing process can be done in daylight. There are a bunch of different kits to use depending on whether you are developing color or black and white film. You'll definitely need a few other items though: storage bottles, a decent thermometer, acrylic gloves if you want to keep chemicals off your hands and I've found a couple of collapsible funnels incredibly helpful. I have a graduated cylinder set with several different sizes. One thing I am careful about is keeping anything that touches fixer away from anything to do with the developer - I learned the hard way that inactivating your developer prior to using it is a bad thing.
Some folks like a sous vide or similar to control temperature, but frankly I just use hot water in a sink and monitor the developer temperature that way. Although there is no doubt that developer temperature matters, it's not THAT critical so long as you're following directions and starting out right. I also have a set of rubber tongs for removing excess water from the film prior to drying.
For a decent overview of the process I learned from this video on YouTube (and probably no coincidence that my first developer was Ilfosol-3 as a result!). It's a nice demonstration of the mixing and agitation techniques needed.
The process is basically filling the tank with the appropriate liquid in turn (developer, stop solution, fixer, wash) at the right temperature and for a suitable time and agitating at specific intervals. This is where the art comes in - sometimes you'll use a higher or lower temperature, sometimes a longer or shorter duration, sometimes you'll agitate every 30 seconds and other times every 30 minutes! It's all down to the specific film and developer you are using and the look you are trying to create. My mentor said to me once that the developer may have more influence on the final result than the film emulsion, and I think he may well be correct in that statement. Thankfully there is a wealth of information out there, both from manufacturers and from the general public. The Massive Dev Chart is something I refer to whenever I have a new film stock, but I also have my own handwritten notes where I've calculated optimal times and temperatures for my commonly-used film stocks. Truth be told, after 6 years of this I can develop pretty much all of the film I shoot without referring to any notes, but I do make use of a calculator spreadsheet of development times for when I reuse my color chemicals (time is increased by 2% for every 36-exposure roll developed).
If I have tips it's mostly about being careful and linking back your results to the process - label bottles NOT just the bottle tops (which can be swapped...), watch temperature and time, plan ahead with your equipment and make sure you have time and space to get things done. Once you're in the middle of a 10-minute development with agitations every 30 seconds, you're pretty much tied to that developing tank unless the house is burning down, and if you don't have space to safely hang a full strip of wet film (which is over 5ft long) that will suck immensely. I use my shower door frame. Lastly, the final rinse should be with a detergent of some kind (even clear hand/dish soap will do - one drop in the tank filled with water is enough - but some kits include a final rinse solution) for 30-60 seconds, and then I carefully but thoroughly squeegee the film dry as it hangs with two loooong single swipes top to bottom.
Scanning film is a whole other thing...and I'll save that for another post.