I have various favourite bacari for the little snackie things. I visit several every trip, and I'm looking forward to more treats this June.
They are all a bit different from each other and the easiest thing is to pop in and watch for a couple of minutes to see how each one works.
I normally go at lunch time and don't drink alcohol. My spellings below are in Veneziana, the local dialect of Italian.
At my favourite, Cantinone del Vino Già Schiavi, which is towards the south end of Dorsoduro opposite the Squero where gondolas are built and repaired (look out for all the geraniums in the window boxes - they were originally Austrian craftsmen) there are no seats. You just wander in, wander up to the glass display of the labelled prepared cichèti - drool - and point. The lady in the white coat (been there for years and years) behind the counter actually has a little English (very little) but the bartenders just behind her certainly have good English and will help if needed. You can either stand around inside using your hands to hold your plate in one hand and a glass in the other (try it!) or there are a few little shelves at various places along the walls, but generally do what everybody does and take your prizes outside and put the plate on the wall of the canal and watch the world go by. You pay when you receive the food or drink. Take cash. Prices are moderate and taste excellent. Be adventurous. If there is a small chance you don't like something don't go and get more of that item. It won't have cost much per item. But like Dim Sum, it can add up if you don't stop. Dorsoduro 992, near Ponte (bridge) San Trovaso.
At ae Do Spade near Rialto Market and Pensione Guerrato, you can take your plate and sit at a little table if there is one free or they will come to the table and take an order (more expensive from the menu at the table). Also perhaps the world's smallest toilet I wonder. The cichèti tend to be very traditional. Friendly staff, some speak English, better if you try some Italian. Pointing works well.... Prices add up quickly. Tends to be very busy. I've never taken anything outside the door. Ordering at the table gets you more larger dishes primarily of fish, and that is a good way to spend a lot of money. San Polo 860, on Calle do Spade.
do Mori just nearby is open less reliably but tends to have food all afternoon (or at least longer than many), very tasty even though they do have surimi "crab legs", lots of fun, not cheap. They have been there longer than anybody else with cichèti. A bit dark inside even in mid day. Nice folks. San Polo 429, Calle dei Do Mori. Either one or two tiny tables outside too.
It is hard to go very wrong. Ask your hotel for their favourite bacaro.