if it's about indicating you move to another topic, i am sorry, but I dont really agree with Nour, in my opinion, you cannot employ "l'essentiel" . If you say something like "l'essentiel, c'est que ..." it would mean more something like "the main point, the most important point is ..." . So it's more used to summarize, or draw a conclusion about what you said before, and not to introduce a new topic.
The french equivalent for "anyway" would be "de toutes façons" / "de toutes manières" and not really "l'essentiel"
In a formal context (talk, lecture .. ) you could use some expressions like " Maintenant, je voudrais vous parler de ..." ou "Maintenant, je voudrais aborder un autre sujet" ou " Passons maintenant à un autre point (un autre sujet) " .
In a casual conversation , you can just say something like "Autre chose ! ..." (abridged form of "Je voudrais vous parler d'autre chose"), or simply " Je change de sujet ! ...." and then start with the new topic.
Example : you are on the phone with your boyfriend, who is at office, talking about your next vacations. Suddenly, you realize there is nothing left for dinner in the fridge : you will tell him "Oh ! Autre chose ! En rentrant, peux-tu nous prendre quelque chose à manger pour ce soir ? Il n'y a plus rien dans le frigo !"
If something comes suddenly to your mind, and you want to mention it before you forget , you can also say " Oh, pendant que j'y pense, peux tu nous prendre quelque chose a manger pour ce soir ? "