Find a route with decent Pax that none of your competitors are flying and fill that first. Don't move to another route until you satisfy the demand on the one(s) you've started. Try to avoid being in direct competition with the others at first. And yes, invest in your CI (but not more than 15% of your income for the first few game days because it won't increase rapidly at first anyway, and you need that income to invest in aircraft). I see you are at Oslo. I think it extremely unlucky that there are five airlines based at such a modest hub.