Like the good old lady says, practice and hands-on experience are the primary factors that'll count! You'll be able to write better scripts only over time.
Most importantly, don't restrict yourself to one or two tools like Selenium, TestComplete. You don't need to be an expert at every testing tool, but it will be very beneficial if you get a hang of other tools like ranorex, appium, qtp, rft, etc
All the best :)