Hey guys, I just finished setting up my quad(kit from rc bazaar) . The downside is that one of the motor tends to start a second or two early, while the other three start at the same time. I tried calibrating it with Libre pilot.  But didn't work. Anyway I took a leap of faith hoping I could control it using roll and pitch.  But within a second of starting the quad as in min throttle, the speed started to increase on its own. I lost control and it crashed. . Props broke and lost a cap. 
Any solution? I'm really sad as it was my first project. 

Try reflashing the firmware. If that doesnt work, Try switching the Esc on that motor with another Esc of a different arm.

I flashed the firmware more than two times. . But I have yet to switch the esc. Also I forgot to mention one more prob.  It's that when the quad took off it started changing direction on its own.  Is that due to different thrust produced by the motors?

Yes most probably

I am facing the same problem, top tip would be get better props and a grass feild, the problem is with the tuning... Have u set min and max throttle setting on your esc?
Here is a small check list as to what u should do when u build a quad:
1. Make sure each ESC is collaborated with the min and max throttle
2. make sure u take it off in attitude mode without any other settings like a to +
3. Make sure all other sticks except throttle is at dead centre
4. Make sure you have a soft ground which will not cause damage to anything (grass feilds are the best to test the as your props would survive the crash)
5. Be ready for a crash anytime and always carry more props than what you need
6. Make sure that you remove props when you hook the quad up to the computer
7. Start with PID settings of someone else who is having a "stable" flight(if you don't know what pids are it would be understandable as to why you're having such a difficult time with the unstablility of the 250 quad) don't break your head around PID settings just yet learn how to fly and then we will talk about pids

@rathi thanks a lot. Unfortunately I will be able to proceed only after my exams get over. Will report back results. Thank you @darshan too.

HEY BRO CHECK YOUR FC DIRECTION IF ITS CARSHING ON LIFTING