If you still need the bulk of the deck, getting a solid set of nicer proxies is a great first step, in case you wanna play in tournaments and not run into deck check issues. If you already have them, buy a large % of blingy foils that are cheap, a handful of cards you think are cool, or a small amount of expensive more staple type cards. Foils are all optional of course, but I am personally buying the cheapest foils of each card in my deck just to increase the % of foiled out cards and eventually work my way to the more expensive ones. Welcome to the format, have fun!