Okay, now for some actual advice.
What size brush are you using? The details are a little messy. I'd suggest using a smaller brush for now, but keep in mind that learning to make a nice, sharp brush tip will pay off a lot more in terms of versatility.
The colour scheme seems a little bland at the moment, mostly because of the colours. I understand that you're going for a dirty, gritty camo, but grey, tan and flesh tones just make it look really boring. Try sprucing it up with some details like squad markings (in this case I would go with a shade of blue, it would stand out the best against the tan), electronics with lights (see if anyone you know has any spare marine bits, or even make some small ones yourself using scrap bits of plastic), and the like. Just make sure you don't got overboard, and don't use too many different colours for the lights.
Another way to remedy the monotony of the colours is to improve upon the camo. As of now, it's extremely sparse, and consists of only the main colour and one splotch colour. Add another colour (Graveyard Earth would probably work best in this case), and even add some small flecks of colour to beak up the empty space and make it look less uniform.
As for the models, they too are a bit bland. Is this your first squad of minis? Even if they are, you should to more than just the barebones assembly. Try to add stuff like the aforementioned electronics, scopes (can be easily made from any spare lasgun/ laspistol barrels), etcetera. Also, I'm not sure why the sergeant has a grenade launcher drum.