One thing I'll recommend has nothing to do with skill sets, but strength conditioning. Years ago before I stepped into the mat I realized that the average weight was 185 - 200+. That's pretty ridiculous for LWs. So I spent an entire year bulking up because I refused to let bigger folks out grapple me based on pure size and strength. While they're bigger, we're more agile and quicker. Just watch Marcelo Garcia.
You'll have more confidence. Of course all the while you'll be gaining experience...EVERYONE gets submitted. One of my first experiences was one of the raddest...I got Ippon Seoinaged into an armbar by a more experienced grappler...lolz! I was LOLing in the air onto the mat cuz there was absolutely nothing I could do. Cool stuff...