If you have naturally black/dark hair like me, go a few shades lighter first. I personally don't like the black-to-blonde transition; ombré is supposed to be a smooth gradient between shades that are close to each other, not a straight line of two contrasting colors. For me, I went through a long process of getting the right shade of brown, so if you have naturally black hair, it's most likely not going to happen in just one sitting.
This is how I gradually lightened my hair prior to going ombré. I'd say it took about two years, since I dyed it a couple more shades other than brown. I wouldn't recommend bleaching it, as it looks too unnatural and way more damaging.
If you're a hair novice like me, purchase a product that's meant for ombré. I bought one in the shade 060 (medium to dark brown) and it comes with a brush applicator, which actually provides a gradient effect that the ombré look is supposed to have. Instructions are fairly simple; comb vertically for a more subtle look and horizontally for more intensity. I started off combing my hair horizontally only on the tips. I let the dye sit for a few minutes then gradually worked my way through half of my hair. I waited a couple more minutes then combed vertically just a little more above the previous section. This allowed me to achieve a gradual transition from dark brown, brown, to blonde.
Overall, I was pretty satisfied with the end result. This picture doesn't do it justice. Trust me, it doesn't look this orange in person! Also, just a side tip: ombré looks 10x prettier with beach waves or curly hair. What I do every day to lessen the damage is I french braid my hair when it's damp and sleep with it overnight to achieve this natural-looking, heatless hairstyle. I've learned from my mistakes by straightening and curling my hair on a daily basis before.
So as long as you don't have a line separating your black and blonde hair, just about anyone can rock this trend. Don't be afraid to go bold; changing up your look once in a while gives a boost of confidence. :) Happy styling!