How do I invite people so they actually say yes?

You want invitations people actually accept. Most invitations fail for reasons that have nothing to do with how much people like you, which is the first thing worth knowing, because it is usually the first thing assumed. First, be specific. "We should get together sometime" is not an invitation; it is a kindness. A date, a time, a place converts it into something answerable. Vagueness puts the work of arranging onto the other person, and that is where it dies. Second, make it easy to decline. An invitation with no exit is pressure, and people avoid pressure by avoiding you. "No pressure at all if it is a busy week" measurably raises acceptance, because it lowers the cost of saying no. Third, ask twice over time. One unanswered invitation is not a verdict. Most people who did not come were genuinely busy and slightly embarrassed, and are waiting to be asked again. Fourth, invite to something already happening. "I am walking Saturday morning, come" is far easier to accept than a thing that exists only if they agree. Fifth, name why them. One honest line about why you want their company does more than any amount of arranging. Who would you ask, if the asking were easy?