You will get better responses if you let us know what kinda game your playing.
Varying your play is important but it differs greatly from cash games to tournaments.
If you are having trouble getting people to respect your bets, you need to A)make fewer of them, or B)make them larger (more scary),while showing more good hands. Like you said, if you try to steal every hand, people are going to call you down. You need to pick your spots and make proper plays for each situation. You want to create an image of a dangerous player that people don't want to play against. If they can play against you after the flop without being forced to make tough decisions, you are not achieving that player image.