Hi there, you staying in hotel or AirBnb? Any food criteria to be considered?
Area that i would recommend to stay would be in Avenida da Liberdade area, expensive but super central.
5 de Outubro, Avenidas Novas, Roma and Alvalade also nice areas to look for hotels or accommodation.
Best Ibis (cheap hotel chain, comparable to Travel Lodge) https://www.google.pt/maps/place/Hotel+ibis+Lisboa+Liberdadeemail@example.com,-9.150316,15z/data=!4m2!3m1!1s0x0:0x5a04baf4b8adde57?sa=X&ved=0ahUKEwjwlqPyw6PSAhVH6xoKHZbKCbAQ_BII6gEwHg
is dead smack in central Lisbon, but in one of the nicest/expensive/quietest neighborhoods ever.
Walks there a lot to do, you can walk a lot nearby the river side and get lost there quite easily. Prepare yourself to climb and descend quite a lot... LIsbon is know as the 7 Hills city for a reason.
Places to eat there's a ton and nowadays we're refurbishing the old markets to be something more similar with the Spitafields market, a mix of food and traditional stalls and shops. Mercado da Ribeira has a lot of restaurants inside with everything at a reasonable price.
Drop me an PM if you want more info and if you want to meet up while you here