Both of these excellent poems deal with pastoral imagery, or the simple delights of the countryside and the closeness to nature that is promised in one of these poems and questioned in the other. The speaker in "The Passionate Shepherd to His Love" is eager in painting a highly idyllic picture of the various pleasures that the countryside can offer his love, such as "beds of roses" and "A gown made of the finest wool." However, the nymph in "The Nymph's Reply to the Shepherd" is not so easily seduced by such attractive images, pointing out that "flowers do fade" and all of the things the shepherd promises "Soon break, soon wither, soon forgotten." A good way to focus on how you can compare these two poems would therefore be to explore "the romantic getaway" and the different attitudes of the two poems towards this. You might like to think about the following statement:
Comment on the romantic getaway through comparing and contrasting "The Passionate Shepherd to His Love" and "The Nymph's Reply to the Shepherd."
This would allow you to explore the difference in views between the two poems. Good luck!