To keep your credit score and credit rating in good standing make sure you're responsible using credit that is made available to you.
Never spend more money on your credit card than you're able to pay back quickly.
To raise your credit score you should always try to pay more than the minimum payment on your credit card to help get the balance paid off as quickly as possible.
This shows you're good at paying your credit cards back and are responsible with credit which can lead to a higher credit score.
Avoid taking out too many credit card either as applying for more credit can actually lower your credit score.
When you apply for any loans or credit cards they'll be a hard inquiry put on your credit report which also lowers your credit score.
So only apply for loans and credit cards if you need the loan or credit card.
If you already have poor credit and can't get loans or credit cards you can get a secured credit card where you put money down as a deposit to secure the money on the credit card and you use the secured credit card just like any other credit card and if you use it correctly and pay back the balance like you're required too then the use of the secured credit card can help to raise your credit score.