I am sure you have already checked some lessons on this topic. However, don't worry, this lesson won't bore you or keep you just silent. It is going to present you a real hard time and a real good challenge to you. So be ready to face it.
Many players begin their day by doing regular exercises or songs. They play the same exercises on and on which is in my way boring and not interesting. Well, I am not saying that it is wrong to do it. What I am saying is just make it a little challenging if you spend more time doing your exercises. But, how? Yes! Now you get to the point. Well, be patient, I am going to say it, don't worry. Okay, now let's just stop beating around the bush and get straight to the point.
To accept the challenge take an elastic closed loop (for e.g. a rubber hair binder usually to bind ponytailed hair). Take that loop and insert it into the index finger of your fretting fingers. Twist it around so that it stretches. After the twist, insert the loop into your middle finger, twist it again like earlier. Then repeat the process onto the adjacent fingers (ring and little) respectively. After fixing the loop to the fingers now start doing the exercises and songs that you do daily normally. You will surely suffer this state. As you try to force your fingers for freedom the loop will try to stop you and retard you movement.
You won't be the same player you used to be with the loop remaining to your fingers, will you? And vice versa. If you do this everyday as a daily exercise I am sure you will change your playing and take it to the next step.
Hope you liked this lesson. Keep playing, and challenging yourself!