It is impossible to give one single outstanding advice which will be applicable across all fields of physics and in all countries.
One fairly important thing if you want to stay in academia is: Stay on good terms with your PhD advisor. He or she will write letters of recommendation for you for several years to come and might be able to promote you in different settings as well. The way of keeping your advisor happy will vary from advisor to advisor, so you will have to be alert to what he or she expects from you and make sure to deliver on that.