Is it ok to use premium gas sometimes in my nissan altima or a gas additive?

Yep, it's ok to do that.... But... Chevron with 'Techron' has been proven to help clean injectors and valves! .. An additive containing Techron will help .. *IF NEEDED!*

use what your owners manual says to use and nothing less or more.my owners manual says use only 87 octane,and premium is NOT RECOMMENDED.also my manual states:it is NOT NECESSARY to add ANY AFTERMARKET fuel additives,and if used could cause damage to the fuel system.just use a high quality gas.have i used fuel additives?YES,i have used most all of them!could i tell a difference?NO.have i used premium fuel?YES.could i tell a difference?NO!so,i now only use what the manual says to use,and i go to the same gas station to get fuel!mixed reviews on this!!Oh,and i have different vehicle than you have.mine is 2000 F-150 4.6L supercab,just turned over to 309,000 miles.

It is more important to use a good quality brand of fuel than to use higher than specified octane. Read: http://www.toptiergas.com/