You can get a good feel for the Catskills—which aren't as packed with attractions as most other regions of the state—in just a couple of days. If you're driving, it's not difficult to combine a trip to the Catskills with excursions into the Hudson Valley. Woodstock, for instance, is just a few miles from Kingston and Saugerties.
Focus on either the northern or southern Catskills. Woodstock, which has a smattering of shops and restaurants, makes a good base in the northern Catskills. From here you can easily go hiking, canoeing, kayaking, tubing, or fishing, or visit Kaaterskill Falls. The ski resorts are accessible from here as well: the Hunter Mountain ski area, for example, is 19 mi to the north and the Belleayre Mountain ski area is about 30 mi to the west. The Catskill Game Farm, about 25 mi north, is also nearby. Another option is to make quick jaunts into the small villages in the area, including Mount Tremper (which also makes a good base) and Phoenicia or, closer to Belleayre, Fleischmanns, Margaretville, and Arkville. Regardless, be sure to devote a few hours to exploring Woodstock.
In the southern Catskills, the area around Monticello has a few good lodging choices, including a magnificent inn in Forestburgh and a golf-focused resort in Kiamesha Lake. If you head west, you can see the site of the famed 1969 Woodstock music festival on the outskirts of Bethel. The area is known for golf and fishing, and the fishing town of Roscoe is about 26 mi north of Monticello; if you're an avid angler, you'll want to base yourself here. The Catskill Fly Fishing Center and Museum is in nearby Livingston Manor.
During the warm-weather months, follow the two-day itinerary for the southern Catskills and then head to the northern Catskills on the morning of Day 3. Drive north on Route 17/Interstate 86 to Route 30, and take that east into the Belleayre Mountain ski area. Explore Fleischmanns, Margaretville, or Arkville in the afternoon, or go hiking or mountain biking. Spend Day 4 exploring Woodstock (driving through Mount Tremper and Phoenicia on the way back to your base) and leave Day 5 for Kaaterskill Falls. During ski season, spend only one day in the southern Catskills and devote much of the rest of the time to the Hunter Mountain ski area, the Belleayre Mountain ski area, or the Windham ski area. In between time on the slopes, check out the surrounding villages. You may also want to spend a day in Woodstock.