You've already taken the first step! When you see yourself as a "half glass empty" kind of person instead of "half glass full" type person, you've already done the biggest step--recognizing you have a negative outlook. Trust me, as I am sure you already know, the world has ENOUGH negatives to last about fifteen lifetimes. So looking for the good in a situation really helps. In that same vein, watching yourself for trigger words like "I can't"... also helps. Alot of people cut their own possibilities short by constantly using "but I can't ........." How do you know you can't if you've never tried? "I can't" is usually actually yourself saying... "I'm afraid to try." So get a little adventurous! Try new stuff! Go new places!! Try new foods!! Its an entire world of discovery out there!!
Also remember... even negative experiences are positive. How you say? Well, they teach you the things you DON'T want and need in life. Let's say you're dating your 16th deadbeat in a row and keep going "WHY do I need this kind of man in my life?! What the hell am I trying to do to myself here?!" Well... you're TRYING to learn that you don't need someone that is a "deadbeat" to feel needed. You can partner with a good person and be together because you WANT to be, not because you NEED to be. This is just one example, but begin working on seeing "negatives" for their "positive learning experience" instead of being the "worst possible thing in the whole world!!!"
Also remember, people are drama addicts in today's world. If you don't believe me, look at modern TV! Look for those places where you seek out negatives just to make life more interesting... and weed them OUT of the garden of your life! Treat your life and person and home with respect!! Treat it like a sanctuary!! You work hard for your home and life, treat it like its worth treating well! You'll soon see your attitude changing--but remember patience too. It takes at least 21 days for any thought pattern or behavior pattern to change into a "habit." So be gentle with yourself.
Good luck and I hope this helps!