With seafood:
If I have fishing, then a workboat working teh highest hammer tile.
If no fishing it's a worker if I have a tech and something for them to do (farm, mine, resource, road).
No workboat, no immediate improvements then it's a scout or warrior depending if I have hunting.
If NO Seafood. play the map
Regarding Futurehermit's non-preference for coastal starts, I respectively disagree. I prefer them because
1) Most of the time seafood is present which is great for health, food, and commerce.
2) Often the happy cap early on blocks working food, and I like to work those 2 commerce tiles (3 for financial) when the cap has been reached.
3) Trade route yield is always higher.
4) Harbor. 50% boost to trade route yield and up to three bonus health (crab, clam, fish).
5) Sailing. Allows trade with your own cities even if far away. This allows faster and more efficient REXing. Also lighthouses offer the ealiest food improvement (until civil service or Biology).
6) Option of the Great L:ighhouse and Colossus.
7) Defense. Basically you are protected from attack from barbs or the AI from at least 1 if not more directions. Usually one or 2 cities protect your capital from attack at all. The downside is you are succeptible to Barb Galleys.
8) Rarely have I ever encountered a coastal capital with insufficient early production.
Now, come later in the game, post Civil Service, and internal capital may be better if you have alot of cottages. Simply move the capital.
In short, I always find coastal starts to be extrememly powerful early commerce centers. The exception is if a land locked capital has several precious metals or several floodplains for cottages.