minecraft recommends oracle’s java engine so let’s do this the right way

1) download minecraft.jar
2) install oracle’s jre
3) create a launcher > in fact there is an easier way > the launcher will get the binaries :)

2) let’s use a ppa for that:

apt-get install python-software-properties
add-apt-repository ppa:webupd8team/java
apt-get update

update-alternatives --config java
and select Oracle’s JVM as default

you can short-cut all this by using:
apt-get install oracle-java8-set-default

3) install a Minecraft launcher:
add-apt-repository ppa:minecraft-installer-peeps/minecraft-installer
apt-get update
apt-get install minecraft-installer

to change the skin:
online:
via minecraft.net

offline:
create a folder in your .minecraft folder called
/home/%YOU/.minecraft/resourcepacks/%NAME-OF-RESOURCEPACK/assets/minecraft/textures/entity
in there create a steve.png folder

to change your name (offline only!)
inside /home/%YOU/.minecraft open the launcher_profiles.json
under your profile find the “display name” parameter and edit it.
THIS MAY GET YOU BANNED ONLINE so be sure to have a copy of the file ;)