If you just want to get some excellent, high utility Magic cards, we recommend Fetch Lands, Dual Lands, and/or Shock Lands, as your mana base is one of the most important aspects to your deck. Look at Triomes if you’re using 3+ color decks. Good land cards will help boost any deck.
From there, Mana Rocks are another way to ramp and boost the consistency of your deck and spellcasting.
Further recommendations are highly dependent on what type of deck and colors you are playing, as well as the format. If you have a color picked out for your deck, we recommend browsing the specific color sections to find cards that fit with your theme or deck structure.