I've seen when I don't expect things.. great things happen and I'm very happy
When I'm expecting them nothing great happens
I want to build an attitude in which I don't expect great things.
I do want to be happy and successful but I think it will be easier to get there if my expectations are less.
Please give advise that what should I tell myself to build such an attitude ?

My motto is "I set my standards pretty low that way i'm never disapointed"
Works well for me. But I don't know how to change someone else's views. Most people would tell you to be optimistic but you seem like you want to be a pessimist.

Oh and I know what you mean when your least expecting it something amazing happens! Just keep your mind side tracked from the thing you really want to happen. e.g. if you want a relationship

Be yourself. Expect the worse, and hope for the best.

Setting realistic goals and achieving them will build your confidence,once you do that,you can aim higher...

Once upon a time you could not crawl,but you tried and it happened,then you walked then you talked and learned how to play and reason... set yourself up for success,and step up the pace...

In relationships,you teach people how to treat you, show respect,gain respect,be a friend to gain a friend..

If you never try to reach just beyoond your grasp how will you ever know just how brillent you really are...

There are stumbling blocks everwhere,look at them as learning experiences,what did you learn from this,so the next time you can do it better..

These are just some of the things I learned from my own meadering experiences.