I've never found that using or not using one's credit card actually increases one's credit score. It seems HAVING available credit, being current on any carry-over balance, and not having a high utilization rate seems to be the thing that effects the score in relation to credit cards - but I haven't found that they care whether you don't use a credit card for 6 months or more - just as long as you have it.So others here have given good advice on how to look for no-fee cards. Once you have them, that doesn't mean you have to charge something on them each month.I would also say - you might want to hold off on any "investment property". It doesn't sound like you have reserves to handle if you had an investement property today and hit a worst-case scenario. I think you'd be better off focusing on more of an emergency cushion - 3 months isn't much in today's world.