Formal:
* Je parle anglais. (I speak English.) This is the most common and straightforward way to say it.
* Je suis capable de parler anglais. (I am able to speak English.) This is a more formal way to say it, emphasizing your ability.
* Je maîtrise l'anglais. (I master English.) This implies a high level of proficiency in English.
Informal:
* Je sais parler anglais. (I know how to speak English.) This is a more casual way to say it.
* Je peux parler anglais. (I can speak English.) This is also a more informal way to say it.
In a question:
* Parlez-vous anglais? (Do you speak English?)
* Pouvez-vous parler anglais? (Can you speak English?)
The best choice depends on the situation and your relationship with the person you're talking to.