An overall piece of advice is to pack your bike as lightly as possible. The lighter a bike, the nicer a ride. If you must bring a lot, e.g. because you want to sleep out, pack the heaviest things as low as possible. And make sure to make the weight even on both sides.
On most regular bikes it’s best to pack the heaviest items at the luggage carrier at the back. More specialized touring bikes can handle quite a bit of weight on the front fork without the handling being negatively affected – and some bikes even become more stable with weight in front.
Make sure that bags and luggage are securely fastened. Check frequently if anything is shaken loose, especially if you are cycling with untested equipment.
Make sure belts and such are well away from wheels and other rotating parts