How to beat the london system
First, you have to understand that you can't expect to win straight from the opening (unless your opponent plays dubious). Your goal is to develop your pieces, castle and fight for the center. The real fight comes in the middlegame and maybe in the endgame.
Against the London System You can play the Grunfeld setup with d5, Nf6, g6, Bg7, b6, Bb7, c5, Nc6. It's pretty easy to learn and your plan is Qc8-Ba6, then advancee on the queenside.
The other setup I recommend (and i play) is 1. d4 d5 2. Bf4 Nf6 3. Nf3 e6 4. e3 Bd6
5. Bg3 O-O 6. Bd3 b6 then Bb7 and don't let White play e4.
Then there is 1. d4 d5 2. Bf4 c5 and if you play Nf6 (Benko which is recommended here, or any others) apart from d5 you can play 1. d4 Nf6 2. Bf4 c5 3. e3 Qb6 hitting b2.
Hope this helps and if you have questions email me or write here.
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Quite large question:)
In the course playing against d4 sidelines, after trompovsky, the 2nd section gonna be betaing London system :)
I think a London system player must learn Trompowsky attack also. So that he can meet everything with 2.Bf4 except 1...Nf6.
Against 1.d4 Nf6 Trompowsky attack will be better. Another advantage is Trompowsky will take your opponent to out of the book in the 2nd move
Both the three indian defences are useful and solid against the London system; and let's not forget benko gambit pawn-structures!