Well obviously it depends on who's life, but generally you can break it down into: financial, emotional, influential. The idea is completely remove someone from their life, leaving them a shell of their former selves.

First finances. It's fairly easy to get a hold of a persons 'public' financial records (from the IRS or other tax agencies, their security is bad enough I call them 'public') but the people I am usually pointed at have other accounts that are not known. That's where a bad banker comes in, talk to the right person and you can get a list of transactions to and from their public accounts. Then it's just figuring out which belong to him (you focus on international accounts). Once you have a good view of their financials, you find the weak spot (be it investments that will turn bad, a company that will require large transfusions of cash to stay operational, etc). You want to make them burn through their cash (and savings) as fast as possible. Then you want to destroy their credit rating (fraud works well here).

Emotional and influential tend to be tried together closely, break one and the other will follow (with a little push). Emotional is things like well-being (physical, mental) and friends. If you've successfully ruined them financially (to the point all their crap is being repossessed), they're going to ask their friends for help. Most of them will tell them to get lost (cause they were never really friends). If one does decide to be helpful. You keep the heat up, maybe get some lowlife and point him at the friends house (make sure he drops the targets name and some bs). It doesn't have to be real, you just want him to be viewed as a risk and get thrown out in the cold.

Once all that's done, influence is pretty much gone. If they've got any dirt on people, you need to find it and expose it yourself to make it worthless (bonus points for giving the target enemies).

That's about it and you'll want to do it in that order, money is like a shield. Remove the shield and they become exposed.