Step 1 - New blood on the bench
While neither condoning nor condemning the firing of Gardy, it was way past time for a change. His style just wasn't doing it anymore. The team was fundamentally unsound. The talent is there, but it seems like they don't know how to play the game. Throwing to the wrong base, missing cut-offs, getting picked off, bunting when its not needed, etc... This team needs a field staff that can get these kids to play baseball, not whatever the past 4 seasons have been.
Step 2 - Veteran leadership
This team needs a Torii Hunter type - a veteran who is both willing to help teach the kids how to play and ready to smack 'em upside the head when needed. Gardy never started throwing players under the bus until Torii left, and even then it was the younger players. If the team dives into the free agent pool it needs to get a veteran with some fire.
Step 3 - Commit 100%
Fuld, Mastro, Escobar, Schafer and a few others are nice players, on a contending team. As reserves. They are not everyday players, especially on a rebuilding team. Either sign veteran starters to be gap stops or get the kids up here. Granted injuries didn't help, but the future needs to be with the big club. This goes for the rotation as well. This team should be going into year 4 of a re-build, but its only going into year 2. The Band-Aid method didn't work, do it right. And we fans need to realize this also.
Step 4 - Don't be afraid to be a copycat
Take a look at St. Louis, Pittsburgh, KC, Oakland, Tampa and a few others. They play younger players until they become expensive, and then have younger players ready when they lose those expensive players. Or invest wisely. San Francisco has a terrible offense, but oh that pitching staff and defense. Minnesota used to be the team to emulate in the reload method, maybe they will remember how to do it.
I'm sure there are things that could be added to this re-build plan, but I feel it would be a start and after another year or two this team will be viable again.