I got my first gray hair when I was around 18. Looking back on pictures I see how terrible my hair looked. I had auburn hair and colored it much darker to avoid looking brassy, but ended up looking pale and tired. If you are not familiar with the process it might be wise to go to a salon and tell them you have never colored your hair and intend to continue coloring your hair at home. The colorist should offer some tips and possibly give you an incentive to return periodically.
Now 20 years have passed and I have a lot more gray hair to cover. I got tired of coloring my own hair and have my hair done by a colorist. Once I settled on a hair color, I only go in for touch ups and sometimes add low or hi-lights.
Not to say there are not great hair color kits that are relatively easy to use. When I color my hair at home, I always wear a shirt I don't care if I get hair color on and put down an old towel just in case some dye lands on the floor or sink, then clip up my long hair while waiting for it to cover the gray.
Good luck on your decision!