First determine if it's a true slice, or are you blocking it left. With a slice you see the ball continue to turn away from the target line (banana ball). A block just goes straight left. With a slice it helps to know what makes the ball move - side spin, and what creates side spin. Most likely you're cutting across the ball at an angle, but there's a lot of other moves that may cause that.
Best advice is to get with a good instructor, but if you want to work on it yourself get someone to video your swing in slow motion and watch the path of the clubhead through the ball. Lots of drills out there to work with once you determine why the ball is slicing. Be patient - depending on how long you've been hitting a slice, it's going to take a lot of work to break that habit. You can spend a ton of time trying to figure it out yourself, whereas a good instructor might notice something right away.
My personal experience is I usually hit my tee shot pretty straight but once in awhile I start drifting right. After seeing an instructor we determined I was simply getting lazy at the top and cupping the back of my left wrist, which opens the clubface. Still creeps in once in awhile but I usually can correct it on the next swing.
Good luck with it.

25 handicapper and have suffered from a slice. I have recently straightened my drives out by setting the driver head further back from the ball to give more time for the face to square. I also set up more in the heal as on the down swing I tend to hit out of the toe. No expert but seems to be working for me and hitting more fairways. Good luck!

Start with a piece of 2x4 or 4x4 wood just outside the ball, on the target line. Rehearse small swings to get a better swing path. Your slice path will show your club hitting the wood every time. Slow it down, 3/4 swings, before you know it, you're swinging down the line, or slightly in to out, promoting a draw. Be patient, something golfers aren't good at!

"Best advice is to get with a good instructor, but if you want to work on it yourself get someone to video your swing in slow motion and watch the path of the clubhead through the ball. "

Barry hit the nail on the head, you may not have a slice at all. I discovered this myself after a pga pro took a look at my swing while I was testing a driver. He give me the proper driver config for my swing type, but I also changed to my natural strong right hand grip from one that was taught to me at golf academy and its been 280yd rockets ever since. I use to struggle to get the ball to fly straight passed 200 yds, now I'm aiming for the back net.

Hi Matthew, I spent 30 years fading (sometimes slicing) the ball and only recently was able to correct it, and I even draw the ball now! My and other swing fixes didn’t work, and did a free swing analysis on Skillest which I HIGHLy recommend. The instructor was spot on and gave me a grip change, narrow stance, and a steeper swing path as my right arm was getting trapped. I highly recommend seeing a professional, I like Skillest since it’s convenient to do from home when I have time. Good luck, keep grinding

A good instructor should fix your slice fairly quickly. It's usually something in your setup, or just coming "over the top" in the downswing. Start with your grip, alignment and posture and then take slow swings to see your starting lines first. Once thing I've been hearing a lot from instructors is to keep your back to the target as long as you can.

You'll get lots of opinions, but the best advice is always to see an instructor. It will save you a lot of time and aggravation.

Every golfer is different. Let a "professional" take a look at your swing and see what your flaws are and fix them. Best decision you can make.

Leave it to the pros on offering advice. Too many cooks make for a bad recipe.

I was a chronic slicer with my irons. Tried everything from shaft changes to grip changes to swing changes. I went and got a fitting. Lengthened the shaft, small adjustment to an upright lie angle for my swing, the correct size grip and the proper shaft weight and I don’t slice anymore. Tighter dispersion has come through lessons and practice. Get a fitting and see your game improve!

I’m on the other end of the spectrum with a draw or a two fairways over DUCK HOOK! Had my first lesson since the ‘90’s and worked on a new “practice routine” and a new “warmup routine” v. hitting a bucket of balls then running to the tee or just running to the tee COLD! “L to L” was a huge step and totally trusted my PGA Instructor to make suggestions via video. Thinking I already knew everything about my golf game was causing my handicap and confidence to fall apart! I’ve taken a set of (8) lessons once a week for (1) hour lesson and I’m on week (2) ATM…

i agree with others. may be best to talk to a certified golf instructor. Paying a little money can save a lot of time and frustration on trying to fix it on a message board. One thing I have learned is everyone swing is dynamic and unique to them so its difficult to accept what worked for others.