1. No Cross training
Getting fit, shedding weight is no rocket science. We all know that to shed weight the output should be more than the input. If you consume the same or rather more calories what you have burnt, how can you ever loose even a kilo. Maybe you end up gaining weight. Walking for an hour does not entitle you to a cup of ice cream or a burger or a pizza. I never tell my clients to crash diet. What I say, is eat sensibly. Eat balanced, wholesome and nutritious meals instead of junk and dense in calories food.
Every field has and expert and we take their help to do a specific job. Then when it comes to your own body and health, why not rely on experts and qualified fitness professionals, who can customize and design your workout plans to suit your individual needs based on your fitness goals, medical history, your interests, body type etc. Do exercises under careful supervision and guidance. The trainer not only motivates you but also corrects your form and posture. Slight modification in the technique can make a world of a difference. Same exercise that can benefit you, can also injure you if it is done incorrectly. You may just copy a move from a video or seeing someone else do it but if you breathe wrong, do not keep spine aligned or check how you are shifting your weight, etc. you may end up harming yourself. What may be right for your friend or partner may not be suit you. A trainer will change and modify according to your needs.
In your enthusiasm to get quick fixes and fast result, you should not overdo anything. Straining, overdoing, not getting enough rest is not good for your body. Balance is important. Too much, too fast, too soon is the surest path that leads to injury. You have to get adequate rest, eat correct, exercise correct to get your desired results.