The new version of Odoo has just been launched. Odoo V12 is released with lots of new features.
Here is the step by step guide for installing Odoo v12 in ubuntu 18.04.

sudo apt-get update

sudo apt-get -y upgrade

sudo apt-get install python3-pip

pip3 install Babel decorator docutils ebaysdk feedparser gevent greenlet html2text Jinja2 lxml Mako MarkupSafe mock num2words ofxparse passlib Pillow psutil psycogreen psycopg2 pydot pyparsing PyPDF2 pyserial python-dateutil python-openid pytz pyusb PyYAML qrcode reportlab requests six suds-jurko vatnumber vobject Werkzeug XlsxWriter xlwt xlrd

sudo apt-get install -y npm

sudo ln -s /usr/bin/nodejs /usr/bin/node

sudo npm install -g less less-plugin-clean-css

sudo apt-get install node-less

sudo apt-get install python-software-properties

sudo vim /etc/apt/sources.list.d/pgdg.list

add a line for the repository

deb http://apt.postgresql.org/pub/repos/apt/ xenial-pgdg main

wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -

sudo apt-get update

sudo apt-get install postgresql-9.6

Create Database user for Odoo

sudo su postgres

createuser ubuntu_system_user

psql -l

psql template1

alter role ubuntu_system_user with password 'postgres';

alter role ubuntu_system_user with SUPERUSER;

Install Gdata

cd /opt/odoo

sudo wget https://pypi.python.org/packages/a8/70/bd554151443fe9e89d9a934a7891aaffc63b9cb5c7d608972919a002c03c/gdata-2.0.18.tar.gz

sudo tar zxvf gdata-2.0.18.tar.gz

sudo chown -R odoo: gdata-2.0.18

sudo -s

cd gdata-2.0.18/

python setup.py install

exit

Odoo 12 Download from GitHub

cd /opt/odoo

sudo apt-get install git

sudo su - odoo -s /bin/bash

git clone https://www.github.com/odoo/odoo --depth 1 --branch 12.0 --single-branch

exit

sudo apt-get -f install

sudo wget https://github.com/wkhtmltopdf/wkhtmltopdf/releases/download/0.12.1/wkhtmltox-0.12.1_linux-trusty-amd64.deb

sudo dpkg -i wkhtmltox-0.12.1_linux-trusty-amd64.deb

sudo cp /usr/local/bin/wkhtmltoimage /usr/bin/wkhtmltoimage

sudo cp /usr/local/bin/wkhtmltopdf /usr/bin/wkhtmltopdf

Run Odoo Server

Open browser on :

http://localhost:8069

cd /usr/local/lib/

sudo git clone https://github.com/sass/sassc.git --branch 3.4.2 --depth 1

sudo git clone https://github.com/sass/libsass.git --branch 3.4-stable --depth 1

sudo git clone https://github.com/sass/sass-spec.git --depth=1

echo 'SASS_LIBSASS_PATH="/usr/local/lib/libsass"' | sudo tee -a /etc/environment

source /etc/environment

sudo make -C libsass

sudo make -C sassc

sudo make -C sassc install

Restart Odoo Server