"Your yard is very pretty today."
Translation:Tu jardín está muy bonito hoy.
This doesn't work in every case, but try putting "always" after "is" or "are", and if it makes sense use "ser"/"es"; if it doesn't use "estar"/"está".
Por ejemplo, "your garden is (always) very pretty today" doesn't make sense, therefore use "está". Contrast, "your garden is (always) pretty", which could be either "es" or "está" depending on the meaning you are trying to get across.
Spanish does not have a word that is directly equivalent to yard. My speculation is this goes back to the typical Spanish mountain side whitewashed village found in Spain and later in Latin America. The house was arranged around a central courtyard which they call a "patio." There were no front or back yards. So, it is possible any modern style grassy area just gets thrown in with garden (jardin). Anyone want to chime in on this?
Usted means "you". If you wanted to say "your yard" with the formal you/usted, you would say "su jardin..." http://www.studyspanish.com/lessons/posspro.htm
Vuestro is mostly used in Spain, I think, for the "you" plural. In most other countries, they would use "su/sus" and "usted/ustedes" instead of "vuestro/vuestra" and "vosotros/vosotras"