The fact that there are two distinct words in Spanish which may be translated to English 'to be' is a source of confusion for most people learning this language. But it is also one of its most important and interesting aspects. Once you get the hang of it, you will actually enjoy the little differences you may create in the meaning of your own sentences just by an aware choice of ser or estar.
It requires some practice and time to get to that point, though. And until you get there you may, in many cases, avoid this choice. To do that focus on translating the meaning, not the individual words you would use in English. When you do that, you will soon easily come up with multiple alternative sentences. For example, instead of saying:
¿Estás sorprendido por lo que pasó ayer?
Are you surprised by what happened yesterday?
you could say any of the following:
¿Te sientes sorprendido por lo que pasó ayer?
Do you feel surprised by what happened yesterday?
¿Te encuentras sorprendido por lo que pasó ayer?
Do you find yourself surprised by what happened yesterday?
Pareces sorprendido por lo que pasó ayer, ¿es así?
You seem surprised by what happened yesterday, is that right?
¿Te sorprendió lo que pasó ayer?
Did what happened yesterday surprise you?
If it happens that you use ser or estar and are not certain if the verb you selected is the right one, just get more specific. Explain what you meant providing additional details, like when and why. The 'why' depends on the situation, but for the 'when' you could learn a few standard expressions. Always choose the ones that are most close to your speaking style, so that you feel comfortable using them. For example, these phrases suggest temporary meaning: ahora (now), a veces (sometimes), de cuando en cuando (once in a while), ocasionalmente (occasionally). And these phrases suggest permanent meaning: siempre (always), todo el tiempo (all the time), cada día (every day), una y otra vez (time after time).
We can see that learning the alternative and auxiliary expressions brings other advantages as well:
- Your vocabulary will be reacher.
- You will be able to create much more varied sentences.
- You will understand other people better as each person has own style of speaking.
Keep improving on ser vs estar as these two verbs are very important. Alternative phrases will help you with ser and estar only when you speak. You will still need ser and estar to fully understand others. Better understanding of this aspect will come from listening and reading. A natural requirement for it is that you master the conjugation of ser and estar. That's because it is not easy to guess that soy, era and fue are all forms of the verb ser.
More details and interesting tips on ser vs estar may be found in the Ser vs Estar - the Definitive Guide article. This website also offers conjugation charts and exercises for these two verbs.