Para decir que algo es una buena idea, usa should + el verbo tal cual. Es igual para todos (I, you, he), y no lleva to después.
should + verbo tal cual
You should study for the test.
She should see a doctor.
You should try Farville Restaurant.
Not "You should to study more." — say "You should study more.". Sin to después de should: solo should + el verbo tal cual.
Pruébalo: She ___ a doctor about that cough. (should see / should to see / should sees) Respuesta: should see — Después de should, usa el verbo tal cual sin to y sin -s: should see. "Should to see" añade un to de más, y "should sees" añade una -s que should nunca lleva.
shouldn't + verbo tal cual
Para decir que algo no es una buena idea, usa shouldn't + el verbo tal cual. (shouldn't = should not.)
You shouldn't eat so much sugar.
He shouldn't drive so fast.
We shouldn't be late.
Not "You don't should eat so much sugar." — say "You shouldn't eat so much sugar.". El negativo es shouldn't, nunca "don't should".
Pruébalo: He ___ so fast on this road. (shouldn't drive / don't should drive / shouldn't drives) Respuesta: shouldn't drive — El negativo es shouldn't, no "don't should". Y el verbo después se queda simple: shouldn't drive (no "drives").
Should I ...?
Para pedir consejo, empieza con Should + la persona + el verbo tal cual.
Should I call him?
Should we go now?
What should I do?
Pruébalo: ___ I call Amina now, or is it too late? (Should / Do / Am) Respuesta: Should — Para pedir consejo, empieza con Should: Should I call her? "Do I call" pregunta por un hábito, y "Am I call" no es una forma real.
Pruébalo: You look tired. You ___ rest, and you ___ stay up so late. (should … shouldn't / shouldn't … should / should … should) Respuesta: should … shouldn't — Descansar es la buena idea → should rest. Quedarse despierto hasta tarde es la mala idea → shouldn't stay. Should para la buena idea, shouldn't para la que hay que evitar.