Really not expirenced with RTSs either, I mean, Halo-Wars wasn't even a real RTS. >.>
Halo Wars is indicative of the "casual" RTS design approach that has been tried in recent years. It essentially screws over veterans because it waters down the gameplay in the name of simplicity, but it's not particularly helpful to beginners since you still have to learn how to manage an army (and its finances) in real-time, which is the sticking point.
The thing that sets RTS aside from other genres (except maybe turn-based strategy) is multitasking. In any real RTS game, there are lots of things going on at once that require your attention. As a player, you have to learn how to multitask these. There is a temptation to get "tunnel visioned" and focus on one specific battle at a time. If this is a climatic final showdown that will decide the outcome of the game, then it makes sense to focus all your attention there. If it's just a minor skirmish, you need to make a conscious effort to check up on your empire. Another important aspect to pay attention to is scouts. Know your surroundings and what is going on. A surprise attack can be many times more effective than the same attack that someone knew was coming.
As you're learning this, my suggestion is simple: take it slow.
Managing your economy is really all about balancing expenditure. You have only so much money to work with, and lots of different places you might want to spend it. You need to figure out for yourself what your priorities are and how they relate to your long-term goal. They key to a well-balanced budget is to try to spend as efficiently as possible. Try to be thinking about how you're going to spend your money before you actually earn it, and keep a little budget in the back of your head (doesn't need to be exact). Above all else, try to remember to spend your money. It's very common to get tunnel-vision in a major battle and forget to build new units. Those units could well arrive as reinforcements for that same battle.
