I use the Xbox built in lfg service and find it incredibly easy to get into lfg groups there, whether it’s raids, dungeons, Iron Banner, Trials, etc. My advice though is to reply with relevant info and only respond to posts that apply to you. A GOS post might read: “GOS need 3 kwtd, must have 10+ clears.” Before I had 10 clears I responded to other posts. Eventually when I had required number of clears my posts looked something like “20 clears 980 warlock” or whatever. Now I just write “Titan 100+ clears” and get invited almost every time. The more you do an activity and the better you are at it the more likely you’ll get invited.
That works pretty good. If I make a post, I cancel and repost after a few minutes so I'm back at the top of the list.