Check my tapas recommendations. These are all authentic and very easy to enter, nothing fancy. Check them out on Google Maps but out of the top of my head in walking distance + neighbourhood)
Vinitus (Eixample - 20 minutes)
Bar Brutal (El Born - 10 min)
Tantarantana (El Born - 10 min)
Sensi Mezzanine (Gothic - 0-5 min)
These places is all sitting and dining tapas.
If you want to live the real, standing by the bar-kind of tapas where you can find L. Messi undercover on a Sunday, check out
Bar Jai-Ca. You wouldn't rate this a 4 out of 10 looking from the outside but it has some of the best seafood tapas & vermouth that Barcelona has to offer. It especially has a great atmosphere on Sunday mornings/afternoons.
In any of the aforementioned bars you can get a delicious coffee. Ask for a 'cortado' if you like your espresso with a dash of foam. In Spain the rule is: the more the bar looks run down and tastelessly aged, the better the coffee. You order and drink it at the bar and be on your way.