what i think. in order to beat someone, you need patience. the key is to contain your energy so you dont get too tired too quickly. now, if you watch a lot of Ground work, then you ll start to realize that you ll end up on both top and bottom, its inevitable. and when you start standing, what i suggest is to study a Stand up martial art for Balance. Balace is really really helpful, not just for stand up, but for the ground too.
one martial art that consists of a lot of balance is tae kwon do. allthough that is not meant for MMa much, its a really good source for Balance, agility, and strength. you get a shitload of stamina and concentration based on decision making.
i did it and i took in Jiu-Jitsu a few months ago, and i tapped out people left and right only because i had balance and speed. im a guy who weighs about 190lbs and i move like a cheetah. my record is pretty good, beating people who've been there for over 2 years and below.