1. Not warming up.
Warm-ups boost your blood flow and prepare your body for exercise. It literally makes your muscles warm, so they loosen up. This should prep you up for challenges (hence improving your workout) and prevent you from getting any injuries or muscle tears (which will set you back). Walk or go for a slow jog.
2. Not cooling down.
If you stop abruptly after a workout, you'll feel dizzy. Cool down so that your heart rate and blood pressure drop gradually. Do some slow and gentle stretching to prevent yourself from getting injured, too.
3. Not resting on some days.
Your body needs to recover. That's when you'll see results like toned muscles. Exercising every single day of the week really won't do it.
4. Not getting enough sleep.
The hormones in charge of building/rebuilding muscle and burning fat are active when we're asleep and aren't active when we're awake.
5. Not hydrating yourself before and after a workout.
Hydrating before a workout will keep you from getting tired so soon and will prolong your performance.
6. Not eating enough. (not eating carbs, not eating before/after a workout)
Food, like water, is fuel. You'll need to eat the right ones before and after your workout to make sure you have your energy and that you'll help your muscles repair. Also, you're going to need to consume carbs since that's the source of energy, not protein. If you avoid carbs, you deprive your muscles of glycogen, their fuel.
7. Neglecting muscle groups
If you only work selected muscles out, you'll cause imbalances on your body, which can lead to injuries. Make sure you also work muscles groups like your core and glutes.
8. Overtraining in a day
A recent study has found that jogging not more than 150 minutes a week is best for one's health. The scientists also found that the ideal pace is 8 kilometers per hour, and that it's best to jog no more than three times a week. The research was built on a previous study that suggested that long-term strenuous endurance exercises can damage the heart.
9. Texting or socializing
Texting or socializing can give you more rest periods than you would otherwise have if you just focused on your workout. Those rest periods allow your brain and your body to return to normal (the state before your warm-up) so you'll have a hard time bouncing back to your workout. You might even hurt yourself when your muscles aren't warmed up anymore and you strain them.
10. Doing the same workout every time
Your body will get used to your workout, and when it does you'll exert less effort since it has become easier. Have some variety in your workout because that always burns more calories.