Start factory, 3 mex, 4 solar/6 wind, 3 raiders/scouts (to counter enemy raiders and/or raid), push to the centre of the map mex + solar + LLT/defender on every second or so mex depending on mex scarcity, as you go, make a radar at 50% of the map. Keep leapfrogging with radar towers and expansion until you see the enemy on radar. By this stage, a small army of units (any mix you like really) will have joined your push. Establish what the radar dots are using raiders or scouts. If you have a significantly larger army than him, force him back, taking mexes and defending as you go. If not, set up your defensive line just out of range of his. Use radar and raiders/scouts to find the holes and gaps in his defenses, and raid into them while you build up your assault/skirmisher/artillery force, which you should harass his line with where you can without losing units.
Do not go for an exchange of armies or full frontal assault until you can crush him AND secure the territory and wrecks (It's often best to do this with an allies support). There are almost ALWAYS gaps or corners you can harass. Don't go too deep with your army, it will get cut off and surrounded, use raiders for this.
Have cons near the front repairing and building, use them to secure wreckfields with defenses and quickly turn the metal back into units. When I win a battle I usually set my factory to spam pure constructors for a short while, wrecks are THAT important!
If he starts hitting you with artillery, don't jump immediately for a shield, just put a razors kiss in front of all your defences, he will waste all his shots on it.
Your elo will jump 300 points at least.