Three Pillars of Encounters

The three pillars of D&D are Combat, Exploration and Social Interaction. If you want to run a balanced campaign, you should consider having some encounters for each pillar.

When designing an encounter remember that the players should be able to interact with an encounter using their normal abilities, and completing it should usually cost them something - health, daily abilities, potions, etc. If your players do something extremely clever to bypass an encounter without expending any resources or taking any damage then good for them! It still counts as a completed encounter.