I have a few tips and honestly the last is awesome but I haven't seen it on "tips" videos on YT.
First is:
G3A3 with Reflex (or Holo if you have got it) grip & heavy barrel
M26 Mass
And G18 (silencer)
This class is awesome on small maps such as Seine Crossing, Grand Bazaar & Operation USAS (Metro).
M16A3 with Holo, Grip & Silencer
Medkit or M320
G18
M16 is just awesome and M320 is especially good on Grand Bazaar as enemies are often hiding/camping behing walls. You can just blow the wall with it.
First note that this is best for Seine Crossing CONQUEST.
PKP Pecheneg with PK-A (first sight), Bipod & Extended Mags
Claymores
Doesn't really matter but G18 is a good choice
This is much better if you spawn to US side as the building is much closer.
The spot where you want to go is here:
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On that building you can see to flags A, C & D.
It's a very good spot on conquest.