你好,谢谢你的信任!
best此处是副词,副词是可以放在动词前面的,且这样的用法还有很多,比如：
我也是一个有抱负的人. I too am an ambitious man.
我当然乐意帮助您.I certainly would like to help you.
以后你会发现,副词放在动词前面的时候会多过放在后面.
你的问题当中,这个Best,可以放在动词前面,也可以放在宾语后面.即,可以说成：It it not the position that suits my skills best.
你例句中sing此处用的是不及物动词的用法,后面没有宾语了,所以放在了动词后面,如果有宾语,副词还要放在宾语后面.
副词的位置其实很灵活,没有硬性规定说只能放在哪里.比如：
Slowly, he walked into the room.
He walked slowly into the room.
He slowly walked into the room.
He walked into the room slowly.
以上几种说法均是正确的.