Strengthen ur elbow extensors, lattisimus deltoid thigh as these muscle are manly used
while proper diet exercise rest will make u fit

sorry but i should say off season training . you see racers are getting fitter and stronger to meet the unique racing conditions they face on the slope during the race . normal generalized weight training program is not going to get you ahead of the other racers , it is only the general part of your training that all racers do, but not where my question is directed.

"Ski Racing", Wolf Says.
Then he disses the advice the good people gave free - for being too vague.
He says the "snow ski fitness trainers seem to have training methods they keep secret to themselves"
I suggest that if you pay for their services, they'll be all too happy to do what they can for you. Typically this is about £40.00 per hour.
If you are not independently wealthy, you need to get on a national training programme.
You must be prepared to spend all the money you have and then fund yourself for 10 to 15 years without any proper income.

There are 4 Threads that need training.
TTPP
Technical, Tactical, Psychological and Physical.
On top of that you need funding and dedication and insurance, transport, accommodation, lift-passes and an equipment deal.

If you really want to be a top ski racer on the World Cup, and you didn't start at age 8, then you will struggle. I don't mean start skiing at age 8. I mean race school for talented junior skiers.
You need full-time coaching for each thread.

I am a ski teacher and we have to race as part of our training and qualification. That is like the difference between Serie-A and the Pub Team, but we still have to put down a time that is within 18% of the World Champion "Zero FIS" homologation. This has taken me 10 years of training (because I came late to ski racing. I raced slalom kayak when young.) I still haven't got there yet!
That standard is just for a "Full Diplom" commercial ski teacher. It is necessary to go on more training to become race coaches.
There is a big gulf between the World Cup circuit/National teams; and club racing.
You say you want "top-level" ski race performance training.
Some top racers can squat three times their own body-weight whilst standing on a Swiss Ball. Some of them would do one or two reps of that on one leg (probably dispense with the swiss-ball though for that!).
They are strong, powerful, super-agile and use Aerobics, weight training and plyometrics in their programme. One guy I raced with broke his right femur and he beat me down the race course with one leg in full plaster sticking out in front - skiing on his left leg.
(The psychological thread here showing that he would even think of doing this.).
Read about Hermann Meier recovery from having his lower leg amputated in a motor-bike accident. They sewed it back on and he won the world Super-G championship a couple of years later. He complained that he couldn't train so well because of the blood soaking his trainers splashing the floor of the gym.
Read about Jonny Moseley training on a dry-land hill. He dug 1 metre deep holes in the dirt down a 200m steep slope and jumped into each one of them at half-second intervals then climbed back up and did it over again.
http://www.youtube.com/watch?v=TWBkCDdgj2E
The top skiers train on the snow in all four seasons. Many go to Les Deux Alpes in June/July, Tignes in November, then there is the race season, then Hintertux in March-April-May. They will be in the gym every day doing something different every day.

I will pick Giant Slalom as it is the most approachable (but most technical and difficult to do well) of the disciplines, requiring:
Stamina (One minute exertion is a long time for muscles to work on full power. Muscle-stores of Glycogen runs out so you need to train the liver energy.)
Strong Core (No good having huge quads and hammies if they are attached to blancmange-like core).
Amazing muscular strength, strong bones and joints and well-supple connective tissue.
So you need to get a strength and conditioning coach.
You need to go on 12 weeks of 3 sessions a week general weight training introduction and then see what the coach says. Maybe he will say "Do another 12 weeks"
You need to get up to (say) 1.5 times your body weight for full squats, and set a target for getting there. It might take 6 months. So if you are 80kg, you need to be doing sets of 120kg after 6 months from starting. Then move up to 2x your bodyweight that might take a bit longer. You must get perfect technique or you will do more harm than good.
Full olympic-bar squats are the main strength-producing whole-body compound muscle-group resistance training method used by coaches.
For strength, you need to be doing heavy percentage loading. That means 90% of 1RM, few reps (max 6 to failure)and good recovery interval. A good coach will be able to guide you into getting training efficiency. i.e. not training a muscle to exhaustion, but still getting it stronger.
For power, you need to do the strength circuit, but with fast-attack and minimal inter-set recovery.
If you are not already super-lean, you need to burn the fat and than means do the strength workouts but in slow-motion.

After the off-season strength and conditioning, you need to get out in the fields or on to your bike to get the speed work done. Building of lean, fast-twitch muscle fibres.
Learn what training not to do. Stay away from body-building on one end of the continuum and marathon running at the other. These are destructive and counter-productive to the ski racer.
Learn that Army-style beasting training is OK for a short life-expectancy, but you will be finished skiing by age 28.
I have met many very depressed 28 year olds on the ski racer scrap-heap. They never want to see skis again. And they have the hip-joints of a 70 year-old.
You need modern coaching that is outside the National Team. E.G. The team coaches in France just get a new athlete when they break one.

You need to dedicate your whole life to it to get to the top. Nothing that gets in your way can stop you. You either get through it or round it or over it or under it. Racer-chasers will ski-bum round the circuit all season sleeping in cars or on sofas, working in bars or being pisteurs or plongeurs or chalet-boys just to afford the food and the lift-pass. Just to get the FIS points.
You ask
"so what are the parameters that make a difference for the top level competitive skier"
The difference is in the head. The Psychological thread.
It's relatively easy with hard work to get fiter and stronger. Just do more of the right stuff. Psychological? There are very few coaches who are any good at this.
Mostly, they act as filters. Identifying the talent and letting it flow. Too bad if you are not one of the natural winners.
Remedial coaches - that is a different job.
Many athletes realise too late that they were lazy or cut corners in their development as juniors and youths. Having spent 15 years training to ski to arrive at a certain posture and movement pattern, they realise they have to take it all apart and do it all differently.
You have to be mentally tough and endure conditions where the body is telling the mind to give up, without giving up certainly. You must press on even more when the going gets tough.

Try looking on EpicSki.com (tread carefully)or YoucanSki.com (Excellent) for more racer material.
If you are still at school, you need to get your parents to move to Austria to a place like Schladming or Hintertux and get you into race school there.

If you want just one sentence:
Get an aerobic base by running or swimming, then get into the gym and learn how to squat to build lean, strong, powerful musculature and all the time train the mind for mental toughness.
If you want some wisdom:
The way of the master can take 12 years to begin to see clearly. The "quick way" takes 30 years.
(A bit pseudo-zen, but true).
I hope that gives you the basis for future development.
Good Luck
SkiPresto