The easiest thing to check is the boot for leaks that goes from the MAS to the throttle body. If that is not the case, check for spark, then fuel. If you have a clogged idle air valve you could have flooded the car and you will need to take off the valve clean it then do some weird BMW flooding sequence to get it started.
Pull a plug and smell, if it is strong you have flooded it or you can sometimes smell the exhaust when trying to start it, if it is strong then you have flooded it.
Do not start replacing parts, check the free stuff first.