There are many factors that can cause muscle cramps, but there are easy ways to prevent them from occurring. Here are some common causes and preventions of muscle cramps:
Cause: Overexertion – By rushing through sets and not giving your muscles enough time to recover, you can cause a spasm.
Prevention method: Have adequate breaks of 60-90 seconds between sets. If your doing a total body exercise like squats or dead lift with a very heavy weight, give yourself 2-3 minutes to recover.
Cause: Dehydration/lack of Vitamins – Muscle tissue is made up of a large percentage of water, if you don't drink enough water you will cramp up a lot easier. Not having enough vitamins such as potassium can also fast track cramps.
Prevention method: Drink large amounts of water consistently throughout the day, not just before your workout. To test if you're drinking enough water you can check the color of your urine. If its yellow you're dehydrated, if its clear your doing fine.
Try to avoid soft drinks and coffee as they will dehydrate you faster then not drinking anything at all. If you do end up drinking some coffee or a soft drink, try to consume twice as much pure water to rehydrate yourself. Banana's are a good source of potassium, if you cant get a hold of one though, drink a multi-vitamin.
Cause: Not warming up or stretching your muscles – Its surprising how many people in the gym don't stretch and do warm up sets, they just rush out of the locker room into the weights room and start their normal heavy sets. This is a sure way to not only get a cramp, but to also tear a muscle and get injured.
Prevention method: Even if you're late to the gym and its about to close, you must spend at least 20 seconds stretching each muscle. You should then perform a warm up set of 15-20 reps with a light weight before you go all in and start lifting heavy. This doesn't tire you muscles, it just gets blood pumping, ensuring proper circulation.
Cause: Excessive heat: This is the common cause of cramping during summer. Your body's heat rises above what it can cool down and your muscles then overheat, causing them to start cramping.
Prevention method: This relates back to staying very well hydrated, you must make a conscious effort to keep drinking lots of fluids. If it's hotter then normal, you may want to turn the pace of your workout down slightly to prevent your muscles overheating.
With your new found knowledge on how to prevent cramps, you shouldn't need to worry about getting a cramp ever again!
Weight Loss 
There are many factors that can cause muscle cramps, but there are easy ways to prevent them from occurring. Here are some common causes and preventions of muscle cramps: