This is the most difficult to talk about without knowing your own exercise capacity. Usually, the following ideas are helpful:
Your breathing should not be so hard that you cannot talk with someone exercising with you. (Try to get an exercise partner such as a family member or a friend.)
You should feel completely normal within one hour after exercising. (If not, slow down next time.)
You should not feel so much muscle soreness that it keeps you from exercising the next session.
The intensity should be a “comfortable push” level.
Start out slowly each session to warm up, then pick up your pace, then slow down again when you are about to finish.
The most important thing is to start slowly and progress gradually, allowing your body to adapt to the increased levels of activity.