When attacking moscow it will be pretty hard if you don't know what your doing but with a few simple tips I'm sure I can help you.
1. First of all when in siege mode overtake at least one other uplink first of all so you can be allowed a air strike which I highly recommend and second of all it will go towards the Field Intellegence trophy which to achieve you need one hundred uplinks secured by you in any game mode and in any difficulty but they must be held by you at the end of game.
2. Another hint for siege matches is get a rifflemen unit in a transport truck back up with gunships to take down tanks and tanks to take down other transports as we know the transports themselves will take care of the attacking gunships. Plus you should have two of these little armies at each side of the massive walls just incase one runs into a bit of trouble it can't handle which is higly unlikely, this idea will speed things up. Plus it is also good for defending critical uplink alpha.
3.Also my final tip for siege matches is always have artillary on standby just in case and a command vehicle for drone guards.
4. For conquest missions use a riflemen unit inside a transport unit and have a lot of these to secure multiple units and have at least one of any other unit to give support.
5.For assault have groups of every unit together to destroy units easily and have artillary at the back for extra support.