Education, Education, Education. Be it ‘on the job’ education by working for a company prepared to train you, or with a degree and then studio experience.
Don’t just buy software (or worse, use free software) and learn from YouTube. You will be competing against thousands of hobbyists who think they can be a professional designers without any understanding of what they don’t know. Despite popular belief, it is not as easy as that. Three to four years education, then four to five years of experience in a studio is the best way to equip yourself to build a long-term career. Of course, you have to have a talent and aptitude before you consider any of that.