I like to make this trip in middle or late January. Another added benefit is that the eagles are in the area around this time of the year. If you get lucky you might catch one feeding on Salmon early in the day on the banks of the Skagit river. On the flip side the place tends to get pretty crowded with eagle watchers later in the day.
This particular panorama of the fisherman was shot from Howard miller Steelhead park
Directions to Howard Miller Steelhead park
Lat, Long: 48.485595,-121.595778
If you get hungry and you like burgers I would highly recommend the Buffalo Run restaurant in MarbleMount(buffalorunrestaurant.com). I have been there a few times and always liked the food.
In general get a good map of the area and just spend the day exploring. There are so many scenic by roads in this area it is definitely worth exploring.