my first archviz

This is my first arch viz render and I want it to be good.

So please, criticise:)

Looks like a nice start. Here is what jumps out at me.
Lighting is too dark. Easy to fix and probably on your list already.
Proportions are a bit off. The stairs for instance seem like there are too many and too small for a second floor that does not seem that high.
I think what you need is reference images. Not necessarily to copy but to give you some idea of sizing.

You should know that the ionic coloumns can´t be like that just because You want it, them must to have specific proportions, the floor look great! but the scale is too big, as Elson say, You must to review the proportion. I would recommendo You to choose similar colors because a brown wood, a black and withe floor, a blue walls, a red carpet and a dark lamp, them have lot of colors but that is a personal opinion. I think You can turn on the lamp to have a better ilumination, You can do it but You must to work.

As others have said, it’s too dark; however, apart from that and the proportions (what Elson said), this is a good render. Remember that grand, fancy buildings such as this tend to have high ceilings.
Perhaps to add a bit more light you could have the door (which is out of shot, just behind the camera) flung open to cast a beam of light on the room, drawing the viewer’s attention towards the staircase and the red carpet. This would light up the room quite nicely.

How are the materials, on a scale of 1 to 10. That is what I am worried about more.

I think you should also go into detail. For example put flowers and plants somewhere in the room, so it is not that empty. This creates depth, gives an idea of the proportions and small things like leaves make the rest appear bigger. Right now it looks like a small model of a room.
Also I’m confused about why the staircase is that big if there is no door on the upper floor.
I like the Piano, but I can imagine that it’s not a good idea to place it in a corner where the sound has to bounce off one or too walls until it reaches an ear. In my opinion it must be turned around or put somewhere else.