One investment property, looking to expand

[Keaton Vols]

I am 25 y/o, I have a job where depending on overtime, I make around $140,000. I bought a 4 plex a year ago and I live in one unit while saving for another. I put 20% of pay into 401k and have a couple payments totaling around $1000. I will have $30,000 saved up by the end of the year. I’m wondering what the next steps should be going forward to gain another property and expand my portfolio. Any suggestions real-estate or not are greatly appreciated