Don't install random crap from the internet. If you use play store the chance is virtually nil to be infected with malware. You also have to make the active choice to even be able to install these trojans by ticking "non trusted sources" down in preferences.
It isn't exactly hard to keep an Android device malware free. Same as any other operating system with a good selection of programs in the default repos and stores, like Debian, Ubuntu, or OS X. Even if those operating systems don't mandate one supplier of programs only.
If this sounds to hard, just use iPhones and Playstations which are unable to install random crap no matter how much you need it, but at least you're safe.