There are three offensive common strategies: beatdown, cycle, and siege. There are variations on, and combinations of, these strategies, but they are the three primary offenses.
Beatdown decks are designed to run your tower attackers behind a tank card, like Giants or PEKKA. Beatdown decks often include a cheap spell (to help cycle through cards faster or act as a quick counter to an attack) and a higher cost spell that can either boost your attack team or deal heavy damage to incoming attackers.
Cycle decks focus on quick turnover of the deck and are popular with aggressive players. You select one tower attacker, then fill your deck with cheap cards that you can play quickly, which results in your tower attacker popping up more often in your hand than defensive cards in your opponent’s hand. The Hog Rider is a popular card for this type of deck.
Siege decks are built around a powerful weapon, such as the X-Bow or Mortar, that can damage towers from distance. Dedicate the remainder of your deck to defending your towers and weapon of choice.