Finally, always remember to work in a squad. Not only does this keep you in the thick of the fight, it helps your team by focusing you on the complex objectives involved in destroying the enemy Titan. Also, if your squad is effective in combat, you'll all receive a "field upgrade" which grants you a temporary unlock. Use this to test out equipment that you haven't tried yet without wasting an unlock point (you can't change your mind once you spend one).
To recap, our advice so far is to unlock the Defibrillator, RDX explosives, EMP mines, grenades, long sprint ability and the Squad Beacon. After hitting your sixth rank, you'll have a very good idea of which class suits you best, and we suggest you continue to flesh out the equipment in that class. Most of the tier two and three items are quite useful. The fourth unlock you'll receive in each career path is a new weapon - but you'll need to have already gained the three items before it. Practice and dedication within that class will pay off here, big time.
We'll have a deeper strategies for each of the four classes in upcoming guides - 'till then, squad up, listen to your Squad Leader and choose those unlocks wisely.