Hang out with former missionaries, or current missionaries when they’re home. Invite them over or take them out, ask lots of questions and hear their stories.
Get on the mailing list of missionaries from your church, or who are working in places you’re interested in. Receive their newsletters and pray for them.
Go to a missions conference such as:
Consider visiting a missionary overseas and serving them and their ministry for a week or two. Or go on an organised missions trip.