Well it isn't easy. It's something that I've learned to do over time but still don't have quite right. This can be the most frustrating thing about my job and without the right strategy and mindset, it probably will drive a person crazy. But here is my approach to things.
- Be Confident - You would be surprised how far this will get you. If you seem to know what you are talking about, a lot of other people will believe you and do what you say. If you are unsure about what to do next, others will be to and they will find a reason
- Have your facts - It's hard to argue facts. So you have to know what you are talking about and you have to know it before the other guy does. If you are trying to convince someone to do something, and you don't have any facts to back up what you want them to do, good luck making a convincing argument
- Know what battles to fight - You only can fight so many battles. Most of the time, you will discover that 80% of the time, it doesn't really matter what decision gets made. It only matters that one does get made. Therefore, leave you big guns to the fights that need to be fought and don't waste your ammo on things that just don't matter
- Know when to ask for help - There are times that you just can't get the right thing done. That's when you call in the cavalry. You and the person you need to convince probably have someone above you who is in charge of both of you. If you know the battle is worth fighting (and you should after #3) and you know you are right (and you should be after #2) then you need to escalate. There is no shame in fighting the good fight and then calling for help when you need it. Just don't make it a habit.