Don't lie. Don't act/feel guilty. Embrace (in your head, in preparation) the reasons you had to leave as though they were your own. Only talk about the aspects of leaving your job that you have in common with a voluntary resignation on your own initiative.

If you were hiring someone, think about what you would want, and what you want to know. Anything negative in someone's past, you do not really care about it, you just care they are past it and it won't have negative future consequences.

Avoiding the negative aspects of your past is not a matter of deception, but of proving that you are emotionally ready to move on.

On a written job application, which in my experience comes at the end after they think they want you, be honest, but read it like a lawyer and make sure you don't disclose anything that you don't have to.