I turn of my non essentials modules and put on silent running.(and dump heat sinks)
Go for the letterbox and press boost as many times possible but I still get scanned...
Any more suggestion or changes in my routine?
You didn't tell us which ship you're flying and how fast it can boost. [noob] Speed is one of the keys for sure, but also the most important - do not
dawdle. I remember before engineers and thruster upgrades, that even with a lazy boosting ship it was possible to avoid scans. Of course nobody told you to smuggle with a Python using D/C rated thrusters with full of illegal goodies slowing you down even more...
Well, for instance, if you have to High Wake to another system, and this system happens to be obscured by the station, and a flock of security ships are flying around like piranhas, that is when it's getting psychological. If you're flying a ship that cannot outrun security ships, but has more mass, then the fastest and safest way is to Low Wake by boosting away from the station regardless of using silent run or not. This mimizes your exposure in the area.
If you decide to High Wake, fly straight for maximum velocity, and reorient your ship only after you're far enough from security contacts. Like I said earlier, do not dawdle. Doing any zig zag in front of the station, or start to circle around it to have a clean shot to your next system is most likely a fail move.
If you pay attention to the security ships in the area, they usually consist of one or two patrols with several ships per group. You want to be heading out of the station at a high speed the moment when the leading ship of a group(s) is not facing the station entrance. Always monitor their activity if you see them starting to gaining up on you in an attempt to scan you. Depending on the situation of course, but because High Waking takes long time for the FSD to charge, it is sometimes better cancel High Waking and enterer Low Wake instead. It can save you from a succesful scan when the range is very critical and you know you're about to get scanned.