Source: http://www.reboot2elementary.com/discover-elementaryos/things-to-do/
enable the elementary community software repository
sudo apt-add-repository ppa:versable/elementary-update
update your system
sudo apt-get update && sudo apt-get dist-upgrade
make items in system settings > start-up applications visible
sudo sed -i 's/NoDisplay=true/NoDisplay=false/g' /etc/xdg/autostart/*.desktop
install elementary OS community themes pack
sudo apt-get install elementary-dark-theme elementary-plastico-theme elementary-whit-e-theme elementary-harvey-theme elementary-blue-theme elementary-colors-theme elementary-lion-theme elementary-champagne-theme elementary-milk-theme elementary-emod-icons elementary-elfaenza-icons elementary-nitrux-icons elementary-enumix-utouch-icons elementary-plank-themes wingpanel-slim indicator-synapse elementary-tweaks
install all the codecs for your multimedia
sudo apt-get install flashplugin-installer gsfonts-x11 libxine1-ffmpeg gxine mencoder mpeg2dec vorbis-tools id3v2 mpg321 mpg123 libflac++6 ffmpeg totem-mozilla icedax tagtool easytag id3tool lame nautilus-script-audio-convert libmad0 libjpeg-progs flac faac faad sox ffmpeg2theora libmpeg2-4 uudeview flac libmpeg3-1 mpeg3-utils mpegdemux liba52-0.7.4-dev libquicktime2 gstreamer0.10-ffmpeg gstreamer0.10-fluendo-mp3 gstreamer0.10-gnonlin gstreamer0.10-sdl gstreamer0.10-plugins-bad-multiverse gstreamer0.10-plugins-bad gstreamer0.10-plugins-ugly totem-plugins-extra gstreamer-dbus-media-service gstreamer-tools ubuntu-restricted-extras ttf-mscorefonts-installer
file archive management – windows equivalent winzip
sudo apt-get install unace rar unrar p7zip-rar p7zip zip unzip sharutils uudeview mpack lha arj cabextract file-roller
finally, recover some disk space by cleaning up any installation packages that may have been left behind
sudo apt-get autoclean
sudo apt-get autoremove
UPDATE
Skype
wget -O skype.deb http://download.skype.com/linux/skype-ubuntu-precise_4.2.0.13-1_i386.deb
sudo dpkg -i skype.deb
Dropbox
wget -O dropbox.deb https://www.dropbox.com/download?dl=packages/ubuntu/dropbox_1.6.0_amd64.deb
Sublime
sudo add-apt-repository ppa:webupd8team/sublime-text-2
sudo apt-get update
sudo apt-get install sublime-text
Nodejs and npm
sudo apt-get install python-software-properties
sudo apt-add-repository ppa:chris-lea/node.js
sudo apt-get update
sudo apt-get install nodejs
Ibus
sudo apt-get install ibus ibus-qt4 ibus-unikey