Personally, I feel like one of the greatest things about Nordic is that you are stretching while you exercise, so even though it is harder work and WILL make you sore that first time out, you won’t be as sore as you would be with almost any other sport.
However, if you really want to start the season right or come at your first outing with enough to have fun, here are some things I would concentrate on to help build strength in the right areas.
Lunges. This is basically what you are doing all day. There are two types that I prefer. One is the regular lunge where you stick your leg out and have a deep bending walk, hands overhead. The other is the same way, except you put a little jump into it. This works on your explosivity.
Core. You’ll need to keep your core stable in order to drive your legs and your arms. Planks are excellent for this and are extremely efficient at getting your core strong. I also like Russian kicks. You do a regular squat, then you come up on one leg and kick out with the other. It is a real core killer. Really anything that is not a traditional situp is probably pretty good.
Legs. Deadlift, squats, squat presses, which are my favorite. My favorite exercise without any weight is to pretend like you are speed skating. Jump side to side and squat with it. Very excellent to build that thrust work in your thighs.
Here is a pretty decent video on some good exercises for strength training for Nordic. I would take their advice. But you are truly using your whole body, so unless you are just doing bicep curls, then WHATEVER you are doing is going to help you get stronger at skiing or skating.
Strength training for X-Country skiing