guys, how often did you clean your laptop( clear the dust , apply thermal paste)? once in a year ?

Cleaning should be as required la.
If you live in dusty environment, say like the middle east, maybe even every six months require cleaning.
Thermal paste, actually, I only replaced after about 5 years, since there was no issue at all before that.

i am thinking off sending my 1 year old laptop for servicing . i noticed that under power saving mode , it can run up to 46 degree , compared to last time only 41 degree maximum

Laptop cleaning you can do yourself. It's a good experience, too. Just Google your laptop model and see if got video on it.
Unless your laptop is those difficult to open ones, I guess.

i cant open mine , mine is a555l asus , still cant find disassembling video yet. if open the case , must to apply new thermal paste ?

the frequency to clean laptop cooling system depends on the surroundings in which it's used. the bottom line is that as long as cpu/gpu temperatures are not above 85c under loads, you don't need to do it.

as a habit i clean mine once a year. the cpu/gpu temperatures are still below 80c.

To my knowledge.... New thermal paste is required if the old one has hardened, iinm. Or if u somehow removed the heatsink causing the paste to crack, be damaged, or whatever, resulting in it no longer can efficiently transfer heat.
Unless the above happens ,the should not be a reason for you to change the paste.