Long coats need do require much more brushing than short coats, but still require moderate grooming. The long coated needs a good brushing and combing once a week.
The one element that will differ is that you will want to take care to search for any mats (tangle hair that knots up), as if they are not taken care of they can grow larger and larger, until you have a big problem and the mat may need to be cut off.
If you search for any mats at least 1 time per week, you can catch them early and fix them by covering your hands with conditioner and working the mat out by hand, slowly and gently.
The bib or ruff of the long coats may need extra washes as food can become easily attached to that area.
Check the bottom of paw pads. With a long haired Chihuahua, straggly hairs can grow out from between the pads. This can cause discomfort for the dog and additionally it can cause traction issues. Clip any stragglers to be level with the pads.
While there will be light shedding throughout the year, it may increase to a more moderate shed twice per year; especially for that that reside in areas that experience all 4 seasons.
This happens during the onset of autumn when a change in temperature and few hours of sunlight trigger a shed of the summer coat to a thicker winter
The 2nd noticeable shed will be during the spring time when day time hours increase and temperature rise. The heavy winter coat of the long haired Chihuahua will be replaced by a slightly thinner summer coat.