0) Acquire decent measuring tools. Chronograph, Calipers, case/bullet comparator, scale, OAL gauge, tube micrometer (for neck thickness). Don't have to be spendy, just reliable.
0.5) Start with quality brass (ADG, Lapua, Peterson, Alpha). If not available in your caliber, sort and measure what you have. Confirm neck thickness doesn't vary by more than ~0.001 (ball micrometer). Confirm base to shoulder length doesn't vary by more than ~0.002 (case comparator). Confirm OAL doesn't varry by more than 0.005" (caliper). Inspect flash holes for centering and "cleanliness" (uniform if necessary).
1) Find the distance to the lands for your chosen projectiles.
2) Find load data that you trust, using a good temperature insensitive powder that provides good velocities. This can be easy for common cartridges, or involve some skill and knowledge for unique or uncommon cartridges.
3A) New brass
A) Lube inside of neck
B) Run over a sizing mandrel to uniform the neck
C) Clean lube from inside neck.
3B) Fired brass
A) Deprime
B) Wipe the outside of the brass or wet tumble to sparkly. This is personal preference, voodoo, sorta thing...
C) Optional - anneal (I do)
D) Lube outside of case evenly. You have to learn what's "just right". Too little = variable sizing, stuck cases. Too much = variable sizing, dented shoulders. A good lube job is critical to consistent sizing.
E) Full length size and adjust die depth to barely (0.001") bump the shoulder back (once fired), or bump shoulder back 0.001" - 0.003" (twice fired onward). Not critical, but to minimize working the brass, use bushing dies and choose a bushing that will size ~0.003" smaller than the mandrel used in the next step.
F) Expand neck to final size with a mandrel die. ID should be 0.001" to 0.003" smaller than bullet OD. Whatever it is, it needs to be the same for every case (usually not a problem with decent dies).
G) Clean lube from brass (tumble, wipe, sonicate, etc).
5) Check OAL. If too long, or extremely variable (>0.005") trim to uniform length.
6) Chamfer inside of case mouth (VLD style tool) and debur outside if needed.
7A) New load, new rifle, etc. Charge 4-6 cases in 1-2% increments up to max (and perhaps 1% over, but be prepared not to shoot the last one or two). This will allow you to establish a rough "Charge weight vs velocity curve", that will allow you to predict velocity for a given charge weight. Shoot over chronograph.
7B) Familiar load, rifle, etc. Pick a charge weight based on 7A or other similar loads you've tried already, that will give you the highest velocity you consider safe (account for ambient temperature ranges you'll be encountering). Charge 8-12 cases.
8) Seat bullets to 0.020" off the lands as measured in step 1 (or maximum mag length if limited there). Make a note of any inconsistent "feel" on seating, and mark those rounds with a sharpie, and note if they behave erratically on target.
The following assumes you are a good shooter, in good conditions, and have done a good job with the above steps, with minimal load to load variation.
9A) Shoot a 3 shot group over a chronograph that's really small, and has a meaningless ES/SD of 6/3, then post about it on the internet, and call it good.
9B) Shoot two 4-6 shot groups, or a single 8-10 shot group and record velocities. If you did everything right above, and have a quality rifle, you will get an average right around 1MOA, with the velocity you like, and an ES/SD of 25/12. You are done and can load up a pile of good bullets.
10) If you get anything above ~1.5 MOA and 40/20 ES/SD, try a different bullet and/or powder. If that doesn't work, you have a bad rifle, and will need to start troubleshooting it (scope, stock, bedding, barrel, etc).
11A) Start tinkering with your load, making small changes to neck tension, seating depth, primer, powder charge, etc. Make sure to make multiple changes at once. Shoot a single 3 shot group over a chronograph with each variation, see one that's really small and has a meaningless ES/SD of 6/3, then post about it on the internet, and call it good.
11B) Start tinkering with your load, making small changes to neck tension, seating depth, primer, powder charge, etc. Isolate each tiny change, shoot a 5-10 shot group with each, and notice there is no statistically significant change from the groups from 9B.
12A) Take your "half MOA", "6/3 ES/SD" load from 11A, shoot stuff near and far, notice "fliers" and misses, then repeat 11A on the bench on perfect windless days for the life of the rifle barrel, and never get any practical field practice.
12B) Take your 1 MOA, 25/12 ES/SD load, shoot a 10 shot group at 100 yards to zero your rifle. Proceed to shoot stuff near and far in all kinds of weather and wind, taking good notes on conditions and outcomes, until you know your rifle like Quigley.
That's been my process anyway...