[laepelba]

As I am working through my exercise books, I find that I keep making the same mistakes, and I'm not sure why. Here are some sample sentences from each of the two types of mistakes:

Mistake #1:
Ella siempre le miente a su novio.
Les doy clases de inglés a los extranjeros.
El dueño te busca para que le pagues el alquiler.
Les decimos a Juan y Tomás que tengan cuidado.
Juan le dice a su hijo que no vaya a las montañas mañana.
My issue: I can never tell when I need to write the object pronoun AND the explicitly stated object, which sounds redundant to my English ears. When is it necessary and when is it not?

Mistake #2:
Ellas insisten en que vengas a la fiesta temprano.
Él insiste en que empieces la tarea pronto.
My issue: I can't seem to figure out when to use "en". Is it only with certain verbs?

Thank you for any suggestions you can offer!!! (This message is being typed from a boat on the Rio de la Plata, traveling from Buenos Aires, Argentina to Colonia, Uruguay!)