Be realistic, choose a time of day and number of sessions per week that you can easily schedule into your routine.
Feeling stressed about getting to class or guilty about taking time for yourself undermines your efforts before you start.
Concentrate on your workout; Reading a bookwhile using the stationary bike in the gym might get you through the time, but your attention will have been on the book not on keeping your revolutions at a challenging level, or maintaining your heart rate in its aerobic zone.
Choose fitness activities that interest you, boredom is the number one reason for most people failing to adhere to their fitness program. If you lack self motivation or fall into the book reading cyclist set then try group classes or a Personal Training session where the instructor will help provide the motivation.
Choose more then one activity, so that you alternate your sessions. Check Instructors qualifications, these should be readily available and visible in client areas. It is your right to know you are being taken proper care of.
An institution that belongs to a professional regulatory register will be obliged to make sure its instructors undergo annual professional education to maintain their qualifications. This ensures the latest and safest practices are applied to your gym/studio you have a right to expect this when parting with your money.
For most people what works realistically, is 2/3 times per week. Make your sessions last between 30/ 60 mins in duration, work to between 55 /95 % of your maximum heart rate, and utilise 50% + of your bodies muscle mass.
Eating sensibly and to fuel your training is important. Starving yourself will work against you. Stay hydrated in the workout studio/gym. Drink at least 2 litres of water per day. Do not exercise if you feel unwell, have been drinking alcohol or just had a heavy meal.
If you are in pain consult a qualified practitioner, your trainer is not your doctor. Do not take painkillers to mask pain and if you are taking any drugs, consult a doctor before commencing or continuing an exercise program.
Stay safe, stay motivated and stay healthy!