Resources
Before you think about your base's defenses you need to make sure you have your harvesting structures and storage areas built and fully upgraded to what your current HQ level will allow. Basically the more resources you can stockpile the more you can build and upgrade later.
Building Bot
Make saving Cyber Coins for a third Build Bot your first priority as doing so will enable you to build/upgrade three structures at once. Stockpile Cyber Coins quicker by taking advantage of the 'under 5 minutes' rule that enables you to rush to completion any production or defense buildings being built.
Balanced Team
Always look to have a balanced team, if you focus too much on one area you will eventually run into problems. When you are putting together a team look at the bio of the character if you are unsure about them. This is done by tapping on the little '?' icon on the top right corner of their portrait and it will give you information such as level, power, general class info, range, and special ability descriptions.
Defense
Like most games of this type the best defensive strategy is to keep everything close and within range of each other to prevent the enemy from easily picking them off one at a time. A good tactic is to use buildings and walls to obstruct your defenses in the hope it will trick attackers into approaching from a bad angle. Don't move obstacles like trees and rocks unless it is really necessary or you have extra resources to spend.
Attack
Although you will unlock a new character when you complete campaign missions it is more beneficial to constantly fight other players around your rank so you can win more resources and level-up your Transformers. Even if you lose you will still get some XP and resources but you will need to wait a few minutes for your Transformers to recover from the damage they have sustained. Make sure when you are attacking you are aware of each of your characters abilites so you are able to take advantage of them whenever possible.
Scout
Before you attack scout your opponents base by tapping on their defensive items to see their range of attack, and info about them. Look for turrets that can be safely attacked by a gunner class Transformer from a safe distance and focus on eliminating those first. Remember, the timer countdown only starts when you deploy your first unit.
Energy
When you launch an assault on an opponents base keep an eye out for objects that will give you energy when attacked as this will unlock your Transformers abilities.
Shuttle
Make sure that you upgrade your shuttle whenever possible as each additional level willl allow you to take an extra character into battle, and the more numbers you take the better your odds become of being the victor.
HQ
Destroying the HQ means winning all the resources and battle trophies so a good strategy is to place your HQ as far away as you can from the launch platform so you force your opponents to plough through your defense before they can reach it.
Statis Mines
It is crucial that you avoid statis mines because although they will not kill your robot they will put it out of action and let other defensces score free hits.
Shield
If you have been attacked you will most certainly lose medals and your PvP rank will be affected. However you will receive a shield that will prevent any further attacks for a few hours which gives you plenty of time to rebuild and upgrade more defenses.
Special Attacks
Don't waste any special attacks you get from using a crystal at the Space Bridge, make sure before you use them you know what they do as these abilities can only be used once.
Character Upgrades
Plan your upgrades ahead because once a character is being upgraded at the Research Lab it will be unusable until the process has completed.