You may check this link, might be useful:

http://openies.com/blog/install-openerp-odoo-9-on-ubuntu-server-14-04-lts/ 

<==== Updated answer ===>

Hi Dieter, the above link was working when I was posting the answer first time. Anyway the installation is similar to that of v8, only difference is some additional python libraries, which you can easily install. There is a wonderful tutorial on v8 installation, you can just refer that:

http://www.theopensourcerer.com/2014/09/how-to-install-openerp-odoo-8-on-ubuntu-server-14-04-lts/ 

I am just extracting the major steps to set odoo 9 ready for development environment.

Step 1: Install and configure the database server, PostgreSQL

sudo apt-get install postgresql

Then configure the Odoo user on postgres:

First change to the postgres user so we have the necessary privileges to configure the database.

sudo su - postgres

Now create a new database user. This is so Odoo has access rights to connect to PostgreSQL and to create and drop databases. Remember what your choice of password is here; you will need it later on:

createuser --createdb --username postgres --no-createrole --no-superuser --pwprompt systemusername

Enter password for new role: ********

Enter it again: ********

You put the username of current logged in user.

Finally exit from the postgres user account:

exit

Step 2: Install the system library as odoo 9 depends on node-less:

sudp apt-get install python-pip python-dev libevent-dev gcc libxml2-dev libxslt-dev node-less libldap2-dev libssl-dev

Step 3: Install the necessary Python libraries for the server.

The following command will install all the required libraries for Odoo 9.

cd /tmp && wget https://raw.githubusercontent.com/odoo/odoo/9.0/requirements.txt && sudo pip install -r requirements.txt

On the above step, if you get an error in between, some dependent library might be missing, so just install that missing library shown and redo the above step. (for eg: sudo apt-get install python-ldap)

Step 4: Download odoo 9

The last step is to download odoo 9 (branch 9.0) .zip file from: https://github.com/odoo/odoo

Extract odoo-9.0.zip file, then in commandline, cd to the extracted odoo-9.0 directory and run odoo.py as follows:

python odoo.py --addons-path addons

step 5: http://localhost:8069/web

Run odoo 9

The above steps are minimal ones to run odoo 9 in development environment. For setting up in production, you can refer the above detailed tutorial link of theopenresourcerer. You just need to change the steps that download odoo file and libraries, other things you can follow the same.

If you have any issues with the installation, I can help you to resolve. (akhilpsivan@outlook.com)

Hope this helps!

I did that, but could not finish, here my observations following your guide:

1. once you wrote by accident 2 times apt-get install (that was easiest ;-).

2. pip install -r /opt/odoo/server/requirements.txt

throws: Error: You need to install postgresql-server-dev-X.Y for building a server-side extension or libpq-dev for building a client-side application.

I ignored and moved on

3. In lst step, what config file you mean? Howto locate it?

4. You missed to mention howto fire installation and what would be standard admin, since there was no step to put user or pass

Thanks for your help!