I would propose that all lobbyist interactions with elected officials are treated as public communications. No closed doors - if the lobbyist wants to educate a lawmaker on a particular subject, the meeting must be open to the public and on-record. All materials provided to the official must also be made available to the public. This not only provides a forum for interested parties to provide counter points to special interest propaganda, but it also makes expensive retreats nearly impossible if the venue has to allow entrance to the press and the general public.
This also, then, makes unnecessary any restrictions on ex-lawmakers becoming lobbyists as it severely reduces any unfair influence that lobbyists can provide - no private lunches or closed-door meetings between "old friends". An ex-lawmaker's advantage as a lobbyist would be his familiarity with being on the other side of the table, not from his contacts and residual influence (or at least only minimally so).
This does not address campaign contributions, which while often part of the lobbying process, is its own thing. Also, the idea is nascent and nowhere near completely developed, but it provides a solid foundation for moving ahead with meaningful reform.