The Phonex and Chaos armors are the best armours to have while the best weapon is the Nail Gun as it follows it's target and doesn't miss.
Free Mithril
You can get free Mithril at the 'Main' menu by going to the bottom left of the screen and tapping 'Three Free Mithril for either following on Twitter or Facebook'. You will still get the 3 Mithril even if you don't follow it.
How to get free mithril a lots of them
You can get mithril by downloading the games it offers you. Just download the game, launch it and get out and go 2 star warfare alien invasion it will give you 5 mithrils.
Quick Level Up
The quickest way to level up is to play Online mode. You will also get game money, gems and Experience whenever you play Online mode.