VAP,
I am certainly no world-beater, but a world class straight pool lover. I tried to learn the game on my own for 30 years, never succeeded in attaining even minimal proficiency. With some expert help over the past 2 years I am certainly improving, and I can relay what I've been told are the keys to learning this fascinating game.
#1 Become a student of the game. The video's and books mentioned by Wally are a great start. Read them, memorize them, master them. They are not sufficient to become a "player," but definitely necessary.
#2 Play with better players. Take every opportunity to involve/trap the better players into a game; travel if you have to. Playing straight pool by yourself is just practice. The game itself is very different; you must also learn to bring your best stroke, first shot, every time, even after sitting for a while.
#3 Play with worse players. I have many beginners playing straight pool now; it is EASY to handicap (Frank Glenn system), and makes for great games. Just play to 50 if your opponents are not as enthusiastic as you. Spot them enough balls to MAKE SURE they win the first time, and play for very small stakes - they will love trouncing you (subtract 5 balls from their handicap if they beat you, add 5 balls to their handicap if you win). The poorer players will love the opportunity to shoot at everything, and you will have the opportunity to shoot flyers and low probability caroms/kisses/combo's that you would never try against better players.
#4 Start a league if you can - handicapping is essential. Advertise as a league for "real pool players", challenge their manhood.
#5 Practice shots specific to straight pool:
Spot shots with ball in hand; shoot the ball on the spot and get position on the common side-of-the-rack break balls. Its amazing how often this comes up in competition.
Practice pocketing side of the rack break balls (you don't have to have a rack in place, just practice pocketing the balls) from 3 cue ball positions (closer to the side rail than the object ball, even with the object ball, and further from the side rail than the object ball) - use follow for the first and third position, a touch of draw for the second position. Include break balls on both sides of the rack. Also include below the rack and side pocket break balls. I have shot about 45 of these shots a day for a year and am starting to get the hang of it - but still miss in competition sometimes.
Practice shooting "escape the bottom rail" shots. Line up 13 balls along the foot string. Take ball in hand, use a rail bridge allowing a comfortable bridge (ie. cue ball a few inches off the rail), and shoot all 13 into the corner pockets 9 feet away. Willie Mosconi could do this in less than 2 minutes, only touching the cue ball for his initial shot, and getting perfect position for the subsequent shot. You are allowed ball in hand for each shot. I cut 13 to my left, then 13 to my right, then 13 to the left with the cueball almost frozen to the rail, then 13 to the right with the cue ball almost frozen to the rail. I never practice them with the cue ball frozen, because I'm never going to shoot that in a game. These shots are essential if you are to win those "below-the-rack" safety battles.
Practice short-side cuts. Place the object ball just off the short rail, 3 diamonds from a corner pocket. Now practice radical thin cuts into the corner pocket (3 diamonds away) until you can make them in your sleep. Then learn to make them with hard inside and outside English.
Practice safeties. They say that Irving Crane (my initial straight pool idol) would practice playing himself safe for 30 minutes a day. Wally does 10 minutes. I can do about 3 minutes before lapsing into a stuporous coma (its deadly dull). I find my safety play and touch improves significantly the more competitive straight pool I play (when you are punished for your deficiencies it makes you try harder and concentrate better).
#6 Practice your ball pocketing - develop a perfect stroke. All of the knowledge and practice in the world is worth CRAP if you can't pocket the balls. A noted instructor told me that in straight pool, the guy that pockets the most balls wins; and the corollary is that if your ball pocketing percentage is higher than his you SHOULD win (at very high levels this may not be as true). Develop a stroke that is perfectly repeatable, tension- and pressure-resistant, and STRAIGHT. Learn to use it in competition. Once you are down over the ball, ready to deliver your best and most perfect stroke, make sure you POCKET THE BALL. Don't rush and don't take any shots for granted; there is no more grievous error in straight pool than to miss a ball, and leave an open table for your opponent. If you don't get perfect position you can always play safe - if you miss, you are usually screwed.
P.S. - Post too long, I'll bet you are sorry you asked.
P.P.S. - A professional opponent of mine loves straight pool, likes to play to a thousand. You would fit right in around here.
P.P.P.S. - If you are ever in Indy, you can always find a 6 hour straight pool game in my basement - best room in town.