First of all, make sure you have a pair of shoes adapted to your body type and suitable for your running surface. For this, ask a professional for assistance on what to get.
It would be wise to get a Heart Rate Monitor to control your pace.
Make sure you drink water not only during the sessions but also between sessions.
Stretch after each session to optimize your recovery.
From the start, control your breathing while inhaling and exhaling deeply from your abdomen and thorax.
Ideally, try to workout on Wednesday and Saturday or Sunday.
In order to reinforce your muscles, you can for example do the following exercise session once or twice a week. The exercises follow one another with very short recovery sequences (10 to 15 seconds).
You'll initially repeat 2 series of the following exercise (toning and stretching), and as you get more comfortable, add more series and/or add to your workout time.
1- Sitting, with your back to the wall: 45 seconds to 1 minute
2- Jump, feet parallel 90 ° flexion: 10 times
3- Abs, on your back, knees bent, hands behind your head, lift your chest towards your knees: 20 times
4- Flex your right leg, left leg behind, slightly bent and right foot on a chair: 10 to 20 times, then change legs
5- Jump right/left feet parallel (same as for a slalom): 6 times
6- Core strength exercise: lie face down on mat, rest on your elbows, forearms and toes, keep your back flat, in a straight line: 45 seconds to 1 minute
7- Stretching: 1 to 2 minutes to help you recover between laps.
Please do this session at the end of your workout; if its not possible,then do it on a different day. If that's the case, make sure to warm up before you get started.
Please note that nutrition also plays an important role. The day before you ski, your evening meal should include a lot of carbohydrates (pasta, rice) and you should have a large breakfast. Remember to eat enough calories during the day (you could for example have a chocolat bar) and to drink water on a regular basis.