1500 milages maintenance? what else should i change?

[New2GZ]

i bought my bike used. it had 30 miles when i bought it. now it has 1500 milage. so far things i have done to the bike is:
1. changing oil with Amsoil full synthetic at 1200 milage
2. new spark plug with ngk iridium.

what else i should have done to it? do i have to adjust the valve clearance? clean Air filter? etc. im not a mechanic. sometimes the bike has misfiring issue.

also, how hard is it to change the front brake pads? is it the same like cars? i have some experience with cars.

thanks