Acrylic and enamel paints can be an option, possibly paint markers too.
Your project has me a bit confused...usually ornaments are the decoration(s). What specifically do you have in mind? Please give more specifics, we'd love to help.
You can add ribbon or tiny pine cones.
Hi Christy - Here are a few ideas for some Christmas ornament DIYs. Hope this helps and Happy holidays! Hugs, Holly
PS - We have a FREE Advent calendar printable to countdown to the season! You can download it here --> https://pinkfortitude.com/thank/#Advent
here are 30+ ideas! https://www.charlestoncrafted.com/30-plastic-ball-ornament-decorating-ideas/
Are you thinking of making over existing decorations? you could spray paint, decoupage with Christmas fabric, dip in glue then glitter... I'm going to have a go at spray painting then adding an old tatted drinks coaster, who knows if it will work but I will gave fun.