Purchase a set of clubs that fit YOU. Hand-me-down or borrowed clubs are economic, but having equipment that fits you is important in developing good technique. Although, you don't need the most hi-tech, high priced clubs arguably, only the most advanced golfer will notice the effects of cutting edge technology.
Begin by taking a minimum of five or six golf lessons from a good professional golf instructor. Trial-and-error learning (or getting tips from someone at the range) will leave you flailing and frustrated for years to come. Learn from a Pro starting on day one and you'll avoid grooving bad habits and technique that will plague you for years.
Perfecting the fundamentals early on ensures you'll see constant gains in this difficult sport for years to come. Don't hesitate to take further lessons, from that professional, on an as-needed basis. Instruction on the all-important short game is invaluable, and a playing lesson or two with a Professional is the best way to learn crucial on-course strategy. Forget your duffer friends for advice or lessons. That will only provoke good golfing.
Practice, practice, practice. Get to the range at least twice per week. Make a written training schedule that you will stick to. People don't normally use the words "golf" and "training" in the same sentence, but by thinking of your practice sessions as training seems to make it a more serious commitment you're not likely to blow off. Remind yourself that inconsistent or random practice means slow, or no, gains.
Do you really want to get good at this sport? If so, get on a regular training schedule!
Work on all aspects of the game. Find a driving range that has a bunker and/or a putting green. Favor hitting off grass areas as opposed to those turf mats. Work all your clubs, and focus on the problem clubs. Warm-up by hitting a few dozen balls with your "good" clubs, then get to work on target-oriented practice with the one's that give you problems.
Always finish each session with a few great shots.
Play a minimum of two rounds of golf per month. During your first few years in this sport its best to play for practice as opposed to performance. Sure, it's nice to score as low as possible, but don't obsess over score early on. This will lower the pressure on yourself and free you up to experiment and try chancy shots on the course. This is undoubtedly the best approach for developing wide-ranging skills and to foster long-term gains.