Do join a club and go out with people who are more experienced than you. Start by contacting the American Canoe Association. Their website has a long list of local clubs.
Do take lessons, including winter pool classes to hone your rolling skills. Many local clubs have pool session.
Do take a water safety course. It will make you less likely to get into trouble, and an asset to your fellow boaters.
Do consider slalom racing. Like slalom skiing, it’s a safe, fun way to hone your skills by moving your boat through hanging “gates.” Again, the American Canoe Association has competition clubs listings.
Don’t expect kayaking get you into shape. Use it as a reason to stay in shape. Kayaking uses your whole body. You use your core muscles to move the boat with your hips, to maintain balance in rough water, and to roll back up. You want to have bursts of power and endurance in your arms when you need it.
Don’t go right out and buy stuff. Try out a number of boats before you buy one. There are many different kinds of kayaks, for river, lake, creek and sea. And your boat needs to fit your body, too. Go to a boat show, borrow boats from clubs or shops, and talk with boaters. It can take a while to figure out which boat is best for you, and most serious boaters have a couple of boats. Even paddles and lifejackets require some knowledge to make a good purchase. Look on the ACA website under Paddlesports Conferences or the Event Calendar for big paddlesports shows and festivals. Almost every region of the country has at least one a year.