In my opinion, I have always used Mr. Erik Paulson's entry method. Against an opponent from a orthodox stance (left lead), opponent fires the jab cross. You deflect the jab with your right forearm and the cross with your left forearm. If your familiar with the thai stance video that Coaches Yamasaki and Keiser made you can see the forearm deflections.

After you deflect the strikes, use one hand at a time to get the clinch until you have the opponent in the clinch. Keep your chin down when you enter. When "reaching" for the neck always keep one hand ready to deflect or strike back.

This for me works best against an opponent who charges straight forward.

You can drill it by simply having a partner glove up an slowly execute the punches until you get the timing down.

Hope this helps.