But I know I have to be thoughtless to gain peace state of mind
This can not be done forcefully.
I don't focus at any mental image or object or chakra.
Yes, no need to focus on any image as the very source of creation is shapeless, just observe the self.
See meditating only one time is not gonna make any transformation, instead you will have to make you entire life style a meditation.
There are some important points you can follow in Daily Routine:
1: Try to breath consciously, (When ever you see a tree, breath as you are totally connected with mother nature, this body is soon going to be earth, This way you will automatically bow down to everything you see.)
2: Respect all the 5 elements with great respect, also read how water have memory and will help you if drank by one consciously(with gratitude).
3: Every hour remind once that soon there will No identity of you (you will fall dead one day).
4: Keep your spine straight at least few hours a day, this will make a tremendous amount of change in your life.
5: Eat with gratitude that as you took everything from mother earth and will give everything back to it. (Do not eat after 8 p.m. and chew at least 60 times, as your entire life depends on how you eat, also do not watch T.V while eating, no talk over phone, just sit quite and eat)
6: try to make every gesture consciously (karma towards source of creation).
7: 11 minutes 3 session each day, No need to sit and meditate just do what ever you are doing, focusing your breathe, heart beat or any part of you body.
8: Try to sit one hour start with small (just sit and observe the mind, where it is running always and soon you will observe your heart beat clearly and you will feel blood rushing through veins in your body.) and do not try to clear thoughts let them come, just see what is going on soon they will get clear.
9: Last but not the least, Nature gives you tremendous opportunity to attain Deathless daily, which mean when you lay down to sleep (lay down in Shavasan, palms towards ceiling and now see your body, try to be aware of everything in body, after practicing for 21 days, you will be able to see how mind studs down in deep sleep)