To make it easier for the credit card issuer to raise your current credit limits, use this technique.
Start using your targeted credit card (or cards) and run it up near the limit (75%). Buy all your life necessities and monthly obligations on your credit card when possible. All the stuff you were going to pay with cash, debit card, or check anyway.
Pay the card off at the end of the month. Better yet, make two payments if you can each month 2-weeks apart. This helps with reporting lower usage when calculating your credit score.
Do this for 2-3 months before asking for a credit line increase.
This also is a great way to earn additional points or cash-back on things you were going to pay by cash, debit card, or check anyway. Make it easy for the credit card issuer to say YES to your request for a credit line increase