Vague 'I should improve professionally' produces no movement. Picking one specific skill annually — and deliberately working on it — produces career-changing capability over 5-10 years.
How to choose
Look at where you are weak relative to peers at next level. Where might one new capability unlock new opportunities. Specific examples: financial modelling, technical writing, public speaking, data analysis, specific programming language, sales conversations.
How to develop it
Online course as foundation. Practice in current role where possible. Side projects to apply it. Conversations with colleagues already strong in the area. Annual deep focus, not sporadic effort.
Five years of deliberate skill building produces a substantially more capable professional than five years of 'general experience'.