Do these in the following order
1. Find a Good Instructor (It's Priceless)
Someone who can "teach" you how to improve (doesn't necessarily have to be a pro)
Someone that will show you good fundamentals , good offensive and defensive skills, good decision making and proper billiard etiquette.
2. Do Drills and purchase Instructional material
We currently live in an era (unlike 40-50 years ago) that there are multiple DVD and online instruction available to anyone who wants to learn. Don't always go for DVDs by top players. There are several Instructional DVDs or sites by good instructors
ex :
http://drdavebilliards.com/
http://www.bertkinister.com/
http://thedrillinstructor.us/
https://www.zerox-billiards.com/
Drills will reinforce your abilities at the table. Repetition is key. After shooting certain shots dozens of times they become ingrained into your mind , so they become easier to execute when playing. Make sure that when you're putting in time to improve , that it is quality time. Have a structured practice set-up every time you're going to hit the table, so you know what you're working on that day . If you only have 2hrs , make it a quality 2hrs
3. Play different games
NEVER just limit yourself to only 8-ball and 9-ball. To amass several skills at the table, play as many different games as possible.
Straight pool (14.1) , One-pocket , Rotation , Snooker , 3 cushion , Banks...etc
4. Gamble
This is mostly when you get to be a more competitive player. DO NOT get consumed by it, and don't go broke over it . Bet enough to get the nerves working. Will definitely help when it comes to dealing with pressure situations. (i.e playing in front of family and friends, playing in front of a large crowd , playing well when the entire crowd is routing for the other guy...or even...when you make the Mosconi cup team. lol)
Good Luck
......and remember.....PRACTICE PRACTICE PRACTICE