The "easy" route
The easiest ascent route for Tajumulco is accessed from the end of an unmarked dirt road near Canoa de Piedra / Chiaguachin outside of San Sebastian. To summit via this route, get a driver in San Sebastian (Q120-200 to drop off point) and ascend from there.
From this point, it is an hour hike to an obvious camping spot in a large wooded area to the left of the main trail (which joins in from the southeast). To get there, just keep heading up and to the left through deforested pine. The camping spot is about 30-40 minutes from the summit. On Saturdays, Quetzal Trekkers leads groups of people up the volcano via the main trail. Robberies have been common in recent years.
If you do Tajumulco as an overnight and begin from this route, I recommend that you head for the summit the next morning around 5 a.m. Watching the sun rise over all of Central America ranks amongst the best views and experiences that the country has to offer. At this elevation the nights are extremely cold, bring warm layers. No water sources exist, and there is a scarcity of downed wood; prepare for carrying a heavy pack. The altitude of Tajumulco (4220 meters above sea level) causes some people to have problems, but the view is worth the potential altitude sickness. It is recommended to spend the previous night above 2,400 meters to start acclimatization.
If you have any questions about the hike, contact Quetzal Trekkers in Xela
Note: The only reason that I added this route is because it is commonly used by Guatemalans. If you hike with a Guatemalan, they will probably take you up this route. The other route, main route, is far better for actual hiking. Also, several robberies have happen in the past years, and this route may be used to provide a quick get away. I am posting this information just so that people know of the alternative way to summit Tajumulco.
Warm clothes for high altitude and wind. Rain is imminent from May through October. November through April is dry and has far better views. Plan your clothes accordingly.