Thoughts on Staying Positive

So, as most of you know I'm not exactly a real positive thinker. And I've realized this more and more as my situation has been no-so-much-changing over the past several months. And, so, on that note, recently a friend of mine told me that I should be more positive and assertive in my language. Not only would this help me feel more positive and optimistic, it would really help my mindset.
For example, I tend to say things like "I probably should do....."; or "I probably won't...."; or "it might not work out but...." For me, these phrases are a healthy dose of reality. But, reality can be a little overrated (Thanks Nellie!). Although, I think it's good not to be the eternal optimist. Only because you're going to be disappointed at some point - but then if you're eternally optimistic - can you be disappointed? Hmm....Any-who, these old thoughts tend to make me a more negative thinker. My friend told me to turn those phrases into things like "I am going to..."; and "I will..."; and "It's going to work out..."
So, not that it's going to be every day all day thing for me, but I AM working on it but I'm going to need your help! And we can all use a little less negativity in our lives!