What kind of event do you want to hold? Before you think about decorations, it's vital to set your party's theme. Whether you decide to make it a fall pumpkin spice wonderland or a spooky Halloween party, you can only choose decorations after you know your design goals. For instance, a birthday party for a small child needs to be cheerful and full of bright colors. This event also requires decorations that are safe and not too expensive. If it's a posh sweet 16 party or wedding, then you know that you need to take your decorations game up to the highest level and look for luxe accents.
To decide on a theme, sit down with a pad and pen and brainstorm what aesthetic you want for your party. If you need some direction, it helps to get some insights from any people of honor, such as a bride, the birthday boy, etc. Start a discussion and bounce some ideas off each other. Does the birthday girl love pink garden roses? Then take a note of that and include this bloom in your centerpiece plans. In this stage, you should also plan other logistics such as how many decorations you need, how many tables, chairs, napkins, catering orders, and more. All of these should be considered in light of a fixed budget.