I think supplements are great and i certainly use them myself, but the key word here is supplementation. Meaning that supplement products exist to help with what should already be a solid foundation in terms of diet and training.
Most people take a multivitamin, why? Because we're told it contains everything we could possibly need in our bodies. I am here today to tell you why this is a load of BS.
By eating a large array of fruits, vegetables, good quality meats and grains you should already be consuming all your major vitamins and minerals, and consuming them in excess will cause more harm than good. My recommendation - go to your local GP and ask for a full blood screen to see if you're lacking in any vitamins or minerals the ones that are lacking ask your doctor how to supplement them as well as correct dosages.
Some of the vitamins i do recommend include:
We don't always get to see the sunlight. Somehow in the past few years we have slowly become vampires whilst working 40-50hrs/wk desk jobs. Supplementing vitamin D, especially through winter, as it helps with bone density and iron absorption. Unless you work a full time job outside i would recommend this one.
Vitamin B-12 (Vegetarians and Vegans)
We obtain pretty much all of our Vitamin B12 from animal products. There is a small number of vegetarian B12 sources making the likelihood of a deficiency quite high. Consequently, vegans are particularly prone to Vitamin B12 deficiency and need to maintain their intake via supplementation.
Anything else - consult your doctor and ask for a blood test. Everyone is different and understanding your body may be the final stepping stone to reaching your goals. The easiest way to ensure you do not become deficient is to ensure you are eating a well balanced whole food diet.