Tips on building credit for mortgage

Just paid down my CC , & My collections. Cannot get approved for a large credit line. I have 1 secured card for 1 year and 1 tjmaxx $500 Credit line. They declined my increase. I pay on time. I have late payments from recent student loans . I'm back on track. Hope to dispute some inquiries and late payments. I got a personal loan from a bank $500. That I pay every month. What else should I do