Summerize three main things interest groups do to get laws passed in their favor ?

There are definitely more than three but I can help you with the prime/main three techniques/things used.
1)Propaganda, no not the type your thinking of (not the communist Russian propaganda like stuff), I more mean false truths. The general public is very easy to manipulate and information is also very easy to modify. You can tell a person that a new healthcare system will make everyone with a net worth over $1 Million healthcare cheaper, although you can reword that to sound like, 'healthcare will become more effective and will help to improve the quality of life. This system is designed with the people in mind (the rich ones), I believe that if this system is passed then we will live longer and better lives.' See how different that sounds! It makes it seem like everyone is gonna get amazing care and their life's gonna be peachy. Most times false truths are targeted towards poorly educated people. Sadly that tends to be the general public (DEPENDING ON WHERE YOU ARE!!). If you can rally the general public then you in essence have more control than you need.  
2)Spread lies about other laws/systems. Ok so this one sounds a bit confusing, how are you supposed to spread a lie about a law. While one may not directly spread a lie about a law they can make up lies about the complexity of it, say things like 'this law targets only the upperclass and not you, when in reality it targets the upperclass but does more damage to them than help. 
3)Straight up confuse people/distract them. Create a conflict, chaos is distracting. Surround a law with lies and slander and the people who are working to pass it, chances are the general public is going to go 'I don't trust them! Lets pass that other law which is probably miles worse'. Similar to spreading a law, slander about those working on it can destroy it's reputation.