First off you must be highly organized, creative, trendy, and MOST OF ALL RELIABLE. Being responsive to customers 24-7 is critical especially to start and build your base because word of mouth and recommendations will make or break you. Someone planning an event enough to want to hire someone to help is usually going to be demanding and high maintenance. You have to be completely responsive, positive, and listen to their thoughts while managing their expectations skillfully. Always start with a budget and a goal. Have some basic building skills as it will help when you have a client with a specific demand for settings. Sign up and follow trending blogs -- a simple google search will help you find these or here is a start: https://blog.feedspot.com/event_planning_blogs/ This will help you follow trends and get inspired. At the end of a party, even the most basic one, people will remember it and recall a good time if the people are fun, the food is good, and the atmosphere is ideal. Crowded and hot will ruin you. If you are serving alcohol, create a menu with some signature drinks that are fun and ready to go that match your theme. This will keep the bar moving quickly. Hire staff as needed like at least 2 wait staff to serve and clean as the party goes along with a bartender. Often local college kids will fit this bill economically but for higher end there are plenty of professionals to rely on. Local chef colleges can often offer up chefs that are affordable to on-site cater and serve your party. Nothing is better than someone passing along wonderful bites that are freshly made to mingling guests. Make sure the music is not too loud and even a simple mix made ahead of time to keep things lively works if you dont have a DJ or band. Even a local guy or gal in the corner of a backyard party playing acoustic guitar to sing along songs will make the entertainment a hit. You have to be creative about the flow and the content to deliver an enjoyable experience. And as the event planner, always be present and ready to please!
If you'd like to be an event coordinator, you could consider going to college for event coordinating, communications, or marketing. Being a prepared and organized person would definitely help as well. Try and gain experience by organizing small parties within your family or as a coordinator for clubs in college. Best of luck!