Start with something small – that you learn to manage and not risk going bankrupt. Maybe partner w/ an expert [ Pesachim ~ 110 suggest davka partnering, not buying/selling with a successful person to benefit from his success rather than being a source of it!]. So, avoid things that people are selling to you.
I believe Rambam suggests priority of investing in real estate and profession before getting married
Some advices above about worrying about olam haba goes against another rule: worry about someone else’s physical needs first and about your own spiritual ones first. forgot the author, Ch. Haim or someone from Mussar?