I'm writing this because I was shocked... at you, yes you, most of you should hang your heads. In our Jan poll, only 28% had checked their credit file in the last year, and 53% hadn't in 10yrs. This is potentially damaging to your finances - just one error in those files could kibosh them.

The impact of credit files has grown enormously; for mortgages, loans & cards, it's no longer just will you get 'em, but what rate will you get. And these days your file can affect your acceptance for energy, mobiles & car insurance too.

So managing your creditworthiness is crucial, but it's art not science. Just like going on the pull, different lenders like different things; but some things get most going. Full info in my 35 Credit Score Boosters, here are the BIG 5...

1. How attractive are you? Free test.

You don't have a universal credit rating in the UK, each lender scores you differently. You may be surprised by this, especially if you've paid to see your 'credit score' (that's at best just a loose indication, missing crucial affordability data; do read my don't fall for the credit-score hype guide).

In the real world, what counts is whether you'll actually be accepted for products. While it's not what they're designed for, an easy way to test this is to take 1min to use our free eligibility calcs which show your % acceptance odds for lots of products. Do well, and you're tangibly attractive to lenders.

Eligibility Calculators for ...

0% Balance Transfers | Cheap Loans | Cashback Credit Cards | 0% Spending | Cheap Spending Abroad | Credit Rebuild Cards

These calculators' primary purpose is to let you home in on a top deal without hitting your file, eg, as Kelly emailed: "Legend. Used the balance transfer eligibility calc and got 35mths 0%, shifted £11,500 from up to 29.9% APR. I'm in shock thinking of the saving [£4,600 in interest]."

Will this affect my credit history? No. Unlike applying which leaves a mark, our eligibility calcs use a soft search so while you see it on your file, lenders don't. The same's true when you check your credit file.

2. Check your credit file annually and before important applications.

There are three main credit reference agencies: Experian, Equifax and Callcredit.

Best practice is check them ALL at least once a year; if not do the two big ones (Experian & Equifax). You've a legal right to check them for £2, but find how to check your files for FREE or even be paid up to £9.

Once you get it, check line-by-line for errors. If you don't, and there is a mistake, you may be rejected. And if you keep applying elsewhere after that, even once you fix the error, then having so many applications on your form could still mean rejection. So act sooner.

3. 10 ways to rouge up your credit appeal.

Here are the key cosmetic changes to make yourself more attractive to lenders. Full info in 35 credit boosting tips.

a) Get on the electoral roll. If not, getting credit's tougher, as it can cause ID and tracing issues. If you're worried about junk mail, just opt out of the 'open' register. See full electoral roll help.

b) Time it right. Applications stay on files a year, bad stuff (like defaults & CCJs) six years. So if they'll lapse soon, wait before applying. Plus avoid lots of applications in a short space of time.

c) Be accurate about your income. Lenders may verify this, and if it's wrong, you may be auto-declined.

d) Beware joint mortgages, loans & bank accounts. If your credit file is linked to someone else, lenders can see their history when you're assessed, so be careful if they've a bad history. Linking isn't about whether you snog or live together, it's simply from joint mortgages, loans, bank accounts and sometimes utility bills. Related: how to delink your finances.

e) Don't withdraw cash on credit cards. It's expensive & lenders see it as evidence of poor money management. See Is it different for special overseas cards?

f) Never miss or be late on repayments. Use a direct debit to be sure, even if just for the minimum (then you can repay more on top).

g) Check for address errors. Sounds trivial but isn't. An old, technically active but unused mobile registered to your old address, has been known to trigger a mortgage rejection.

h) Beware payday loans, they kill mortgage applications. Some mortgage underwriters simply won't lend to anyone who's had one. See our free First-Time Buyers' or Remortgage Booklets for more help.

i) Be consistent. Fraud scoring is credit scoring's secret cousin. If you've a couple of mobiles or job titles, use the same one every time you apply or it can be flagged up as odd. See fraud scoring info.

j) Get unfair defaults removed. If there's one on your file (eg, you didn't pay a catalogue loan as it failed to deliver the goods), get it removed or it can be a killer. For how see remove unfair defaults help, and even if it's fair, see how to mitigate the damage from defaults.

Are you financially attractive?
Are you financially attractive?

4. To get credit, you need credit.

Would you lend to someone you knew nowt about? How about someone who's not repaid others in the past? No, and nor will lenders.

Credit scoring predicts your future behaviour based on your past. So no credit history, or one that makes you look a bad credit citizen, usually means rejection.

The bizarre solution is to get a credit card, do £50-£100/mth of normal spending (never withdraw cash) & repay IN FULL each month to avoid interest. The safest way is via direct debit so you're never late. After 6mths to a year, you'll start to gain a history as a good credit citizen.

The catch-22 is how to get accepted if you've poor credit. The solution's specialist credit (re)build cards, and our eligibility calc shows which you're most likely to get. The two top picks are...

- Aqua Advance* which gives a £20 Amazon voucher after 2 months.

- Aqua Reward * which gives 0.5% cashback.

Both these are a horrid 34.9% rep APR if you don't repay in full, so make sure you do. If you can't get these, the last resort is the Credit Improver package, which costs £4/mth.

5. What do they actually know about you?

Lenders' info comes from three sources - and they plug in all of these to score you:

(i) Your application form tells them crucial 'affordability info' and more.

(ii) Any past dealings you've had with them. So a lender you've banked with has more info on you - sometimes good, sometimes not.

(iii) Your credit reference files, which include electoral roll info, products you have, court judgments & more.

As for whether they know if you've speeding points, a criminal record and more, see our full list of what they really know about you.

PS: Are you due £100s back from Experian's CreditExpert?

If you paid for Experian's £15/mth credit monitoring service from 2011 to 2014, you may have been unfairly sold part of it. Our Credit Expert Reclaiming guide shows how to get the cash back, as Dee did: "I sent Experian the template letter and received a payment of £243.59."

This article first appeared in the weekly email on 2 March 2016.