The key issue with breaking up is change. No one likes change. Tell her that the two of you are going to transition from where you are now to something else and you wish her well.
Tell her that she's going to need it to fix things when you're not there anymore. Put a bow on it.
Do your whole first date over again. Tell her you wanted to bring her to where it al started and that if you'd only gone a different direction that first date, you wouldn't be together now. And now it's time to begin again, only going that other direction.
I know it sounds crazy, but tell her the truth. Are you shallow and obsessed with appearances? Do you need more time to work on your novel? Do you just plain not like her? Tell her. It's like ripping the bandage off. Hurts for a second, but then it's done. You will feel vastly better and get closure almost immediately. She'll be able to consider the value of your critique, and possibly even be a better person for it.
Be clear that you don't want to date anymore for the reasons "the relationship" doesn't match what you want for your life. It is good to acknowledge them for whatever you admire/like about them and your relationship together but not too much or they don't hear the message about your decision to break-up. A clean split by spending time not talking or seeing each other afterward is important, even if you choose to remain friends in the long run.
Talk about what you need and why. Avoid blaming or using the words "you made me"
Talk to the person face-to-face use lots of sentences with I...I feel, I think, I want. Don't accuse or blame the other person. It takes two to make a relationship work, and two to make it not work. Your attitude can set the tone for the conversation so it doesn't turn into an argument. Make sure you listen attentively don't make it all about being heard. Speak with love from the heart and you'll find the right words.
Just have her casually mention it at the end of the conversation.
What ever you do, make sure you are piece with what you do. No remorse is the best way to get out of it. I agree it is not the most friendly way, but it will feel the best.
It's just tacky to text message the other person to end your relationship.
...population: YOU! Don't use tacky or clicke phrases. A variation of anything ever said on the Simpsons or Family Guy is just bad form.
Even though you might be annoyed, don't blame the other person. Just BRIEFLY but sincerely explain that it's not working and why. The other person deserves to hear a reason.= for the breakup.
Who doesn't love a compliment? The nicest possible breakup might be because the other person "deserves better". For example, if you don't want to have kids and she does, you might be able to lovingly say that an awesome girl like her deserves to be with someone who wants to be an awesome father. You want her to reach her dreams and potential and she can't do that by sticking with you.