Up until now you have likely been performing endurance training that included long, steady, easy efforts on fairly flat terrain. It's important to continue your endurance training 1 to 2 times per week, but now is the time to increase your endurance training pace. Increase your pace by increasing your cadence (rpms) on the bike and increase your foot speed during a run.
Perform your endurance training over terrain that is similar to that of the events you plan to enter. If the course is flat, train on the flats. But if the course is hilly, even your endurance training should be done on hills. Your effort level will be far less then on race day, but your muscles and your mind will be prepared for the course and you will simply increase your intensity accordingly.
You will also want to add some high intensity sprints at the end of your endurance training to simulate the final efforts during competition also known as the "final kick." During the last 5 to 15 minutes of your training, gradually increase your speed and pace. Maintain the effort through the finish and then cool down completely before resting.
These tips can help you move from basic training to the next level of fitness and ultimately help you peak for races or events in your future.