Fly with the lowest frequency possible, but it is recommended to stick to 1.
Use an aircraft that gives the best profit, e.g. a 777 flying at €125 normally gives lower profit than a 737 flying at €285. I personally try to keep the ticket price in the range of ~€200 - €300, so I adjust the plane flying the route if the ticket price is too low/high.
The routes you are describing with fierce competition are best dealt with flying a reasonable sized plane (100-150 seats) at 100% loadfactor. I would recommend you to just experiment with a route to see what gives best result, I don't have much experience with this.
Sorry if it's hard to understand, it is late in the night here
