Best or most efficient way to regain sec status?

coming back to -10 account, what is the ideal way to rebuild sec status now ?

to at least get basic access and no more flashy red

buying tags ? where do u buy them and which ones

killing belt rats in null ?

Security tags will get you to zero, after that you have to fight.
https://wiki.eveuniversity.org/Security_tags

alright thx fren