Defund the FBI, CIA, NSA, ATF, and DEA. They've proven themselves to cause more trouble than to solve problems.
We need public auditing of these organizations. Organization that operate secretly will always provide some refuge for corruption. There are always blind spots for management. If the public has no input, how can we ever trust them?
Accountability is further complicated by the fact that the entity is political in nature, so the FBI has actual partisan backing through politicians, the court system, and even down to individual jurists.
I honestly don't know what the solution is myself.