Let me share a site with you to help you find places to go grouping at. I find it to be very helpful for finding content around my level.
http://www.whitetalon.com/dungeons/dungeonfinder.asp
Levels 1-10 are pretty easy to solo and you gain xp at a nice pace. Past level 10 however, you will notice a gradual decrease in xp gain soloing. By the time you hit around level 15, it will take hours to gain a level by soloing. It is around this time that you are better off either small grouping 2 dot white +con mobs through 3 dot blue con mobs, or full grouping 3 dot white+ con mobs through 4 dot mobs.
Soloing becomes something you CAN do, when you have limited time to play, want to work on an easy quest, or just want to go test some things out, but grouping becomes the main focus of playing Vanguard in order to progress at a reasonable rate. I usually solo in the mornings after work, but try and group on my nights off. That way I can feel like I worked on my progression, even when I don't have time to go into a long dungeon crawl.
P.S. This is one very good incentive for people not to act like asshats in the game. Because this game makes you rely on others to some degree to see progression, it does not benefit a player to anger his community against him. This is one thing I applaud VG about, social responsibilty means something in this game. Griefing comes with a heavy price.