You should maximize your time and experiences with your children. You should document your involvement. If you have been the person who gets them up in the morning, washed, fed, dressed, transported to day care, to school, home, fed, to bed and comforted at night you’ll probably have the upper hand when it comes to a custody fight. If you are also the person who helps with homework, conferences with teachers, communicates with doctors, comforts and nurtures the children, and you do so while not intoxicated, mentally ill, or viewing pornography, it will help your case immensely!
Obviously if you move away from the children, it will be harder for you to perform parenting functions. Obviously if you always work overtime, it will be harder for you to perform parenting functions. Obviously if the other parent is blocking you from having contact with the children you need to seek legal advice immediately to get back into a position of being able to perform parenting functions.
Everyone can learn more about parenting. Every library has a ton of free and useful resources. The internet is full of free information that can help you a) improve your parenting skills b) learn about the needs of children and c) gain insight in how you might better handle the stress of the changes you and your children are facing.