You've used both verbs since your very first conversation, and the rule of thumb still holds: ser says what something is; estar says how or where it is.

ser	estar
identity, origin, profession — Marcos es andaluz.	feelings and states — Estoy cansada.
characteristics — El hotel es pequeño.	conditions that can change — El mar está tranquilo hoy.
days, dates and times — Hoy es jueves. Son las tres.	where people and things are — buildings too: El hotel está cerca de la playa.
where an event takes place — La fiesta es en el hotel.	the result of an action — La tienda está cerrada. Bidu está tumbado.

Location is the classic trap: a hotel, a church, a whole island — anything you can find on a map — takes estar: ¿Dónde está la iglesia? Only events take ser: a party, a concert, a meeting is somewhere, because it takes place there.

Tumbado — lying down, stretched out.