Agents
Unlock the Training Room as soon as possible and make sure you are constantly training your agents their important skills. Use all your Mission Slots and bring all the agents that you can for each mission. The more agents you have, the easier it will be to complete all missions and defeat players. Each type of agent is good at one thing and bad at something else. Take note of an agents strengths and weaknesses before using it.
Stations
Build as many stations as possible. The more stations under your control, the more that your enemies have to disable before accessing your Control Panel. Hopefully they will run out of energy in the process. Upgrading your stations allows you to produce and have more resources. It also makes them more difficult to break into.