You've got the basic shape so you're off to a great start. I don't know anythink about planes except that they fly... so don't know how best you could improve it, but I would recommend searching similar mocs on the pages. Get inspiration from other people's builds. Study them and you will get excellent tips on techniques and detailing. Ask them questions on how they did said techniques, try it out, don't rush and you'll be away laughing! Good luck!
You asked for criticism you here you got some! lol never mind but I do have some ideas. The engines have to be a bit more rounded (if you what it that way) and the the nose it too "pointy" it the nose of the airplane in in front of the airplane. But overall so far so good, the P-51 has to be the most widely built in lego airplane and is one of the hardest, trust me ;)