If you’re new to running, just start with regular running – don’t add intervals. Your goal is to let your body adapt to the basic activity of running, and you should do this gradually.
Once you’re passed the beginner stage of running, you’ll definitely benefit from mixing your runs up. What kinds of runs you add into your training depends on your goals. For example, longer runs build endurance for longer races. Hill sprints build strength and power over a short distance. Fartlek training involves running at a comfortable pace with intervals completed throughout the run.
If you are changing up your training routine or adding in different drills, be sure to go easy at first to avoid injury and allow your body to become used to the changes.