Don't forget you can provide them with valuable information too. It helps if you get to know how Parliament works as well. Naturally you need to present whatever issue you are promoting in the best way possible. There are usually a number of slants that can be taken on any issue - it helps to match these with who you are talking too. I don't think the lobbying methods have altered that much, it really depends upon the issue and the stage of the campaign.
Actions have to be planned so that they can realistically achieve something.
The people who are making decisions are doing so using sound rationale and justifications. Interest groups need to have well thought out policies and well structured arguments before they decide to approach the media and politicians. The ability to second guess the arguments also helps. That is why having long term contact with Government department staff and advisors is so valuable, you can get to know where they are coming from. The important thing is to keep it regular and personal.