There are many things that build a credit score.
The AGE of your oldest account helps your score. You are just getting started - you don't have any accounts that are old enough to help this part of the score yet. If possible, never close your oldest credit card unless there is a very good reason (such as annual fees or high interest rates)
The number of accounts you have had in the past and successfully paid off helps your score - again - you haven't had time to establish this.
Next - the number of ACTIVE accounts that you have helps your credit score. This is why you were told you to get more credit cards. Credit cards are the easiest way to have active accounts. YOU DO NOT NEED TO USE THEM. You just need to have them. YOU DO NOT HAVE TO ACTUALLY GO INTO DEBT. Just use the cards occasionally. You can use the cards for something you would need to purchase any way. Get a VISA or Mastercard credit card so that you can use them anyplace. Then, use the card to pay something you need anyway. You could even use the card to pay for one of your other bills. Set up your credit card to pay for your cell phone then pay your credit card bill with the money you would have used for the cell phone. You would not be "in debt". You would be building credit while buying the things you use anyway. You could do the same thing with gas in your car or your groceries. Buy with the card then pay the card with the money you would have spent on those items. If you get a rewards card, you would even be earning cash back for doing this. Never use more than 10% of the TOTAL available credit you have on credit cards. Using too much of your available credit also hurts your score. Credit card companies usually won't close a card for not being used unless you fail to use it for an extremely long time. Therefore, you can have several credit cards with NO BALANCE and just use them sometimes to keep them active. (I have one card that I haven't used in over five years and it is still active.)
If you don't think you are capable of having a credit card that you don't use - then just don't do it. Your score will build, it will just take a lot more time. If you think you can have a credit card and not use it - then get a couple more cards and use small amounts for purchases you need and then pay them back WHEN THE BILL CYCLES. That is the last important thing. Let the card company bill you before you pay back what you have spent. If they don't bill you, it is like you didn't even use the card and it isn't helping your score. You don't have to use every card during every month. You just need active accounts that you could use and then actually use a little of which ever card you want to.