Try and upgrade your mines as much as possible. The extra energy and titanium will help you build new towers.
Don't upgrade all your defensive building at the same time. This will leave you open to attack.
Save your crystals for drones. This will help you level up faster later in the game.
Join a corporation. They will send you free troops to help defend your base (once you have obtained a corporate HQ). Just be sure to send some back.
Plan your upgrades to happen when you cannot be on the game. This will optimize your build times.
Place one drone building far away from your base. This will make the troops have to move after destroying the rest of your base potentially stopping them from getting 100%.
Don't accept any resources from challenges until you need them. This will provide free resources for later.
Build troops and attack as much as possible. This is easy resources and medals.
Build all of your available towers. This will make you base harder to destroy and provide defense for your resource/ town buildings.
Max out your base as much as possible before upgrading to headquarters level. If you rush higher level headquarters and your base is slacking in defense you will be getting higher level players to attack and defend.
Always make sure your drones are busy. I usually have one major upgrade that takes 6 hours or more, then I use the other drone(s) to do some minor upgrades such as Generators and Mines.