Its important to become familiar with your cards, obtain the necessary ones for your deck, practice regularly, and seek guidance from more seasoned players.
Your best bet is to focus on meta cards like the EDREC top 100, and anything commanding a high price is worth a closer look
Iconic Cards: Counterspell, Ponder, Damnation, Jace, the Mind Sculptor Popular Decks: UW Control, Jeskai Control, Taking Turns, Esper Control 3 Midrange Midrange decks are popularly said to solve problems, not create them. In other words, these decks are sort of designed to be able to win against every archetype, although they wont bulldoze over anything (the way aggro often wrecks control, for example)
Fetchlands are special land cards that allow players to sacrifice the card and pay 1 life to search their library for another land card, then put it onto the battlefield
Archidekt will highlight any errors that break format rules, and let you import and export deck files from MTG Arena