Well, out of all the Pokemon games, I didn't really do anything special for Crystal. I was pretty young when the game came out, I didn't know a thing about Pokemon (let alone natures and IVs and EVs), and for the most part it was all just a "wut" thing for me. So, that aside, I did have some sort of routine in Pokemon play-throughs. Kind of, maybe, not really. But whatever, I'll just drone on in this post and the lot of you won't read it, but at least I contributed. D:<
For all the Gen III games (RSE and LG), I basically chose my starter, went around, and completed the game. Like any ol' non-competitive kid would do. I always chose the starter that looked badass (Mudkip in RSE and Charmander in LG), and I went the basic hyper-offense route that everyone takes. Seriously, who in there right mind would use a Blissey in-game for a purpose other than Softboiled? After I sent my stuff to Diamond, I replayed the games. Once I knew about competitive battling, I only replayed the games to get good-natured legends that I couldn't find elsewhere (the Regi trio, Kyogre, that stuff).
In Diamond, I actually cared about the nature of my starter, but not much else. I ran a four-Pokemon team with two HM slaves, so they were pretty high leveled compared to a six-Pokemon team. After the Elite Four, I started EV training (but I never got into IV breeding), and after like 150 hours of in-game play, I finally finished the Pokedex. I think my Trainer Card for Diamond has 4 stars, which is just sad. Because the only one I'm missing is the underground flags one.
In my SoulSilver, I cared about natures and tried as best as I could to care about IVs, but I cba to get twelve Rare Candies early game and level up my starter to see the IVs. Probably the only game where I caught all my legends with good natures and in Pokeballs. <3
I don't replay my DS games, so I use an emulator for that. And I do the same basic setup, or I speedrun.
This post turned out to be a lot shorter than I thought.