It's often argued that theists start with a belief in a literal deity (for whatever reasons) then try to find evidence to support it. However I think many people do start with what they consider to be evidence first, even if it's not generally accepted as such.
Why do you believe? Does belief necessarily require evidence? If so, what qualifies?
There is no way to arrive at a theistic belief system
through evidence and logic. At some point you have to make a "leap of faith" (or, as it's called in logic, a "jump to conclusions").
This is usually done by bundling up a host of beliefs. E.g. "I believe the Bible/Koran/Harry Potter to be true.".
I'm not sure that there can't
be a reasonable theistic belief, just because we have no existing example. I'm willing to discuss that option, here or in a separate OP.
As a starting point consider:
Observation: galaxies rotate too fast to explain that with known physics.
Conclusion: there has to be something that causes the galaxies to stay together.
Definition: we call that "something" Dark Matter
Observation: the universe exists and seems to have started in a way not explained by known physics.
Conclusion: there had to have been a cause that started the universe.
Definition: we call that "something" god