I just heard using 1st position at "keyword position preference" is a good method to improve "keyword score" with initial campaign
Who told you that? The only way to improve your quality score, which is what I assume you are referring to, is to have ads that get higher click rates. That's what quality is based on, your CTR. Increasing your bid to high values won't do it and I seriously doubt setting a preferred position to first will either. To learn more about QS, read my free Adwords FAQ.
Your QS tells you if you have a good ad or not. If you want to be in the top position, nothing wrong with that. Setting a position preference of 1 will not guarantee that you will get it. It still depends on your ranking which is QS x bid. And if your ad is not of good quality, that is, the click rate is not better than most other advertisers in the first position, it won't give you a good score. Simple as that. Your ad has to prove itself with the searchers by them clicking on it.
You mean to say if you have built an AD that's great and if you do not position that properly (1-3rd position), it will still get good QS easily?