Prior to starting any exercise in your program, always perform a very light warm-up set of the exercise to prepare you physically and mentally. Beginners should use slow, controlled movements with a continuous flow when starting out - avoid stopping - instead keep the movement flowing until all reps are completed. This keeps the muscle under tension for the whole set and is where real strength gains occur. Over many months of training the speed and power of the movement will increase due to the amount of weight being lifted. As a result, the neuromuscular function will also improve resulting in better muscle coordination and an increase in one's metabolic rate that leans up muscle tissue and burns fat more effectively.
When you are first starting out and figuring out what weights are good for you, you'll have to go through some trial and error to find the correct weight. It is my recommendation that before you start any exercise or training program that you seek your doctor's approval and train under the supervision of a qualified strength and conditioning coach to learn the exercises and train with good form. Essentially, lift a lighter weight for between 10 to 15 reps with good form. The 10 to 15 repetition range is based on the principle that beginners should use slightly lower weight for the first month, in order to allow their connective tissue, muscles and nervous system time to adapt to the loading.