I take the same approach as Treymo and Visck, which is to build a team for the regular season. I, too, use a lot of players subject to 15 game injuries, but generally limit myself to taking players with injuries on 2 or 12. It's next to impossible to build a team for a short series and have success throughout the season, as the variety of teams per league is usually too great. Of course, it almost goes without saying that you can't get a ring without first making the playoffs.
I've also experienced a lack of playoff success. I've had many teams finish with the best or second best record in the league, only to get beat in the semis by teams that lost the season series to my team. One quarter of my playoff teams in 12 team leagues have gotten a ring, mostly the result of a higher success rate since the transition. None of my 7 playoff teams in 24 team leagues have gotten a ring.
I learned a couple valuable lessons with my first online team way back in ATG4. It was a post WWII $100 mil DH league. My team had the best record in the league with 98 wins. The next best team had 93. My team was second in the league in runs and ERA and led the league by far in run differential at +212. It lost the season series to just one team. But my team got beat in extra innings in the last game of a best of 5 semis as a result of a set of highly improbable events. My cheapo bullpen by committee, which saved 55 of 74 games and was 19-18 during the season, got torched in the playoffs, including Ron Perranoski, who was 7-4 with a 1.75 ERA with 11 saves in 15 chances, mostly in middle relief, during the season.
The 2 playoff lessons I learned from that team were: 1. That it's difficult in a short playoff series to overcome bad luck; and 2. The bullpen is more important in the playoffs than the regular season.
I still think the best practice is to build a team for the long haul and to hope for the best in the playoffs, with the caveat that in the playoffs it's important to take advantage of any favorable match ups.
P.S.: Below is a link to to a rare (for me) smallball ATG6 $100 mil DH team in Forbes '57 that got a ring. Aside from being a smallball team, what was unusual about that team for me is that I took a chance on the $9.48 mil Larry Walker card (with an injury on a 3). He missed 38 regular season games, including 15 down the stretch when the playoffs were in doubt. Using such a player is like having a ticking time bomb that you know will explode, but you're not sure when, but hope that it doesn't hurt you when it happens. Although Walker was healthy for the playoffs, DH John McGraw, who had an awesome .511 regular season OBP, missed the last four and a half games of a 7 game Finals due to injury. The reason I went smallball was because the league used the "Dream League" format, where managers pick entire teams at a time, rotating picks over 12 seasons, so each manager takes a turn at picking his full team in all 12 spots. That season, my team was the 11th team drafted in a 12 team league. Enjoy!
http://onlinegames.strat-o-matic.com/team/813933