There is to so much you need to worry about. Most of the people speak English. The cuisine is compatible with all cultures and in most of the places you will be asked for any allergies you might have.
Of cause you will need sun protection from April/May to late September and a hat or cap.
Mosquitos won´boter you too much and wild animals you won’t meet outside of the very nice Bioparc (A day at the Bioparc Valencia).
I guess the best recommendation is to bring some really soft and comfortable shoes like Sport or City Sneaker for the walks through the city. The sidewalks are made mostly out of hard stone tiles, cobble or stone blocks (especially in the historic city center). Even though Valencia does not have many days of rain, if the floors get wet it can become very slippery.
Have a great time in Valencia and enjoy !!!