There was a time way back when this was common practice. "I will give you a link if you give me one". To be honest its best avoided now, If the website in question is not within your niche then it will just look spammy.
However there are some cases where this can be a good thing but only if you have a relationship with the other site in some way.
I get almost daily requests for links for the sites I look after, personally I treat these as spam and as such get sent to my spam folder. I would suggest you do the same.
On a side note, Dont worry too much about your DA score, Google do not use it and it is just a Moz scoring system. It is a guide only and does not always suggest your ability to rank well within your niche.
Instead of trying to increase your DA score spend your time developing you site and improving its content. Keep making improvements there and you will see your DA score rise anyway.