Thank you so much for your reply.
I do not expect paying lots of principle now would help my credit, as long as it does not decrease it; that's good enough for me.
Although I just start to learn credit score, I am already freaked out. This thing makes me nervious, cannot stop thinking "will this decrease my score"
@FrugalRican wrote:Good news: Your car loan IS an installment loan and it will definitely help your "installment" history.
Essentially, problem solved.The thing I'd do is have steady payments for 6 - 12 months and then look into refinancing your car for a lower rate and maybe a shorter term as well.
Paying on the principal won't do anything towards your score. It would save you a lot of money on the interest though.
The only caveat around the plan is that some auto loans might have a pre-payment penalty, or are set up to where they basically just apply the additional payment as credit towards a future payment (i.e. no interest benefit). I understand this is rare these days, but it wouldn't hurt to check your paperwork.
The other question to consider is if you have any open revolving debt right now, which typically charge a higher rate and have a higher impact on your score. And, with a mortgage comming up, it's definitely worth considering hanging onto some cash towards down payment.
And obviously, don't pay late, but I think Frugal covered that base 
There's one more caveat: it depends on how the lender records the additional payment.
Absolutely don't specify when you make the payment that you want it applied to the principal... you won't lose much by letting it burn off whatever accrued interest is there and then let the rest be applied to principal (since on any simple interest installment loan, which virtually every auto loan I know of is, you're zeroing out the interest every month anyway).
Here's the catch though: some lenders will push your next due date out, and some won't. What I would suggest is simply doubling up on your first payment, say that's in June. If you just made the regular installment payment, your next due date would be in July; however, where it gets interesting is if your lender pushes the next due date now out to August (mine does), in which case go nuts and you can pretty easily get a 3-4 year installment tradeline for very little in interest payments. Just be aware it won't be the full term because you're going to wind up way ahead on the amortization schedule... really getting a max term loan if pursuing this strategy would've been ideal rather than the standard 5 years.
Alternatively if your lender doesn't adjust the payment date, just pay some extra on it for the first six months and then go refinance somewhere else. That'll mostly or completely negate the first-time buyer problem you ran into... which incidently I suffered too though my own credit profile is nowhere close to as good as yours. Not too much though, there's some breakpoints with lenders on how little they're willing to finance which I think are mostly around the 12K mark, and that would be annoying to run into. I would strongly encourage you to reseach that with whoever your lenders of choice happen to be on your refinance plan if taking that route.
To also work on that installment loan penalty, consider tossing $2500 in a CD at USAA or some other lender and then taking out a 100% LTV loan secured against the CD as collateral. A bunch of lenders will do this, but I suggest USAA as they offer it at a 2% effective APR which is well worth it if you're missing installment loans, and it's about the cheapest possible to finance if you have cash laying around which it sounds that you do.
Not sure who your lender is, but when I had an auto loan opened in Aug 2010, shortly thereafter I had a significant chunk of money to throw at the loan. When I did, WF sent me a letter saying I couldn't pay more than 5 months ahead on the loan. They didn't send any money back. I kept making my monthly payments and the loan was paid off by Dec 2010 (originally a 36 month loan). There's a remark on that account that says "early termination of loan/paid as agreed". It's a positive account in every aspect so I'm not sure what that remark does to the account.
@kjm79 wrote:Not sure who your lender is, but when I had an auto loan opened in Aug 2010, shortly thereafter I had a significant chunk of money to throw at the loan. When I did, WF sent me a letter saying I couldn't pay more than 5 months ahead on the loan. They didn't send any money back. I kept making my monthly payments and the loan was paid off by Dec 2010 (originally a 36 month loan). There's a remark on that account that says "early termination of loan/paid as agreed". It's a positive account in every aspect so I'm not sure what that remark does to the account.
That date with WF has been pushed at at least, mine was 8 months ahead back in March.
I was 2+ years ahead actually. The WF letter just said I couldn't pay more than 5 months in advance. Well I did. Paid off a 36 month loan in approx. 4 months.