Okay some feedback, take it or leave my taste and your taste doesn't have to be the same. These are only suggestions and things that I would do to improve upon this design:
One of the responses mentioned that there are too many design elements here (the 3D bubbles, the coffee-stain/textured circles, etc.) I was also concerned that the design lacked a certain cohesiveness.
I don't think there are too many elements but there are too many styles which addresses your concern about cohesiveness. You have the very modern text for "Scarlett latte cafe" and the shape of the mug, the line on the right and the yellow boxes.... but then you have very large chalk strokes for the handle and well I'm not sure - table? Then there's ink strokes around the brown circles.
While I appreciate the cohesiveness you attempted with the brown circles connected by the red line, I don't think it works and I'll talk more about that later.
How is the placement of objects on the poster? I have not used a grid, and honestly don't know how to create one and design on it. I do use guides quite scrupulously in illustrator though.
Those brown circles, particularly pastries being by its lonesome is off. There's also some strange spacing on the days of the week with Sun being far from Saturday then Saturday close to Friday then Friday far from Mon-Thurs.
I guess this leads to the question, when designing posters and flyers in the future, how can I do so using grids so the nothing is askew and every thing is aligned well? I am not using InDesign and that might be part of the problem.
There are lots of books specifically on this topic so I'm not going to answer it. Check some of the books out.
Okay you didn't ask this specifically but here are some things you should really consider, it goes in a bit with what Scott mentioned about Function.
First thing is "Now Open" appears 3 times, twice hard to read especially from a distance. If this is an important part as I believe it is, it should probably be much larger perhaps only written once but taken up that entire space.
The brown circles: coffee, tea, pastries.... lunch. One of these is not like the others which ruins the entire thing because it ruins your coding. Perhaps instead of lunch you could put sandwiches or salads or soups or add additional "circles" with a combination of these.
The yellow vertical by the mug is really nice in my opinion but I would put it behind the horizontal strip for the hours and make it almost invisible if not completely invisible behind that strip. The reason is because right now you're highlighting Mon-Fri separating them from the Sat/Sun. I don't think this is intentional. I would also give the yellow box the same texture on the bottom half as the top half.
The Logo is a bit unclear. Is the red circle behind cafe part of it? It looks that way but then the red line is interfering with it. Its one thing to have a background with the logo but I would be very cautious intersecting an element with the logo. Perhaps slightly adjust the red line so that the "bend" goes above the "cafe circle". Speaking of which detail is everything so make it café (with an accent).
I kind of like the circles especially in the mug but as I mentioned in comments the one on the top right is a bubble thats coming through the mug... I would crop the right side or move it left a bit. I will say however it makes me think of soap and bubbles not steam or coffee.
Last is those ink outlines and chalk lines. I would just make them normal strokes since everything else is a regular stroke. Maybe even take the line beneath the mug out entirely since it already has the yellow to "sit" on.