In my 20's I would try every weight bullet I could for the given caliber I was loading. Same with powders. Not so anymore. When I buy a rifle or handgun, I usually know ahead of time what the given purpose is, and what weight, and/or style of bullets I will be using in it. Most of my shooting at critters is at ranges of 25yds to out past 400 with proven loads in high octane calibers. I pick the best combinations or powder and bullet weights to get the best overall results for those purposes. I don't run 140gr bullets out of my 7mm STW at 3500fps when I can run a 160gr at 3000fps which will fly better in the wind and hit harder when it arrives even at the longer ranges. Same for my .243, I use 100gr bullets most of the time because they are more accurate in my rifles, they hit harder, penetrate deeper, and I am confident in them should I shoot a coyote at 350yds or a trophy whitetail buck at 85. I'm not saying that there aren't better bullets that might do the same job in a lighter weight, but for my uses these are it.
Most times it is the medium to heavier weights in bullets and for powders it will be similar medium to slower ones for the caliber. For something like a .243 I would use a 95 - 100gr bullet, first choice on powder would be H-4350 or close to it since I know this area produces great results. Brass will be usually Winchester or Remington since I have a ton of each. Primers would be either tried as I come along with the load but the initial testing would be with Win-WLR. I have used them for decades and they just work. Second to those would be CCI-BR2's.
I usually work my loads up sitting at the farm where I can shoot a few and make adjustments as necessary. I always start with the bullets seated out so that they just fit in the magazine and feed reliably. Once I find something promising in both group and velocity, I might tweak that seating depth in increments of .005" deeper. I will go as far as around .035" - .050" depending on the bullet and caliber, but have gone as far as .130" from the initial starting point. Just depends on how much room you have to work with, what your loads are and what your looking for.
Like many have mentioned it isn't simply a cut and dry situation. Far too many variables for that. Once in a great while the planets line up and you pull a given load combination from a manual and it drives tacks. They are usually close, but still need a little tweaking. There have been times when I have worked up a load from start to finish in a few hours, other times in a month or so and after a hundred or so rounds, then I have a couple that I have worked on for more than a year off and on, and still need some work. But I feel those are the exceptions and the average time is usually around 3-6 weekends initially, then a couple of weekends here and there through the year to test in different conditions and temps. I strive for accuracy first, consistency second, and let the velocity come as it may.
With just about any cup and core bullet, hitting 2800-3000fps, your good and most will work extremely well down to 2500fps starting out. Most of my loads fall into the 2650 - 2850fps range in calibers from .243 through 30-06, and the loads will usually print 5 or more shots into less than an inch at 100 and some at 200yds. It depends on how far your shooting, what your shooting at, and what the desired result are supposed to be, when that bullet gets there. For deer up to around 300# a mid to heavy weight for caliber bullet will get you meat in the freezer every year provided you put it where it should go. Bigger critters need more than smaller ones, but your the only one who can decide where to draw that line.