It's not HQ that's different and hard to grasp, it's S&D that's different from all the other gametypes. It's slower and sneakier and with all the forced spectating for the less experienced, you don't really find a groove. This is why it's easy to keep running into the same place and get killed every time.
HQ is the next gametype that requires the most team coordination, where if people don't play the objective, the game won't go forward. HQ would be followed by Domination, which is getting closer to slayer gametypes. I see Sabotage and Domination being at the same level.
We can shift to a faster paced game. Most people have the basics of the maps down and know some strategy. I suppose Domination would be a good way to get people used to HQ, since the objective is to control and protect an area. Get used to controlling three stationary headquarters, move onto one headquarters that moves around. Also, HQ doesn't have immediate spawns, while Domination does.
But honestly, I couldn't play too much Domination at one time either.