A few general observations I've made that may or may not help.

When sharing a city, road, or farm; it is nearly worthless to continue building it. Any points you add will just help the other players. Try to goad them into finishing it for you and wasting their turns. Only add on if you're trying to connect to an adjacent feature in order to take it over.

Building just to add to your existing road or surround your monastery is usually a wasted turn. One point per tile is not that great. However, adding a road segment onto an existing 4-tile road that nobody is on is a 5 point tile and a great move. Claiming an existing feature is better value than adding onto one you already own.

Don't worry about finishing features unless you're low on meeples. Don't worry about finishing cities until the end of the game. Don't get caught up in the magnitude of the end result. Finishing a 26 point city is not a 26 point play. It's a 2 point play. You already had the other 24 and could have finished it at any time. Just watch to make sure nobody else is trying to take over it. The same philosophy applies for roads, except you can truly just leave them unfinished the whole game.

Steal, steal, steal. Taking a feature that someone else started is the highest point play you can make. Play around the edges of their city where a single diagonal tile can make them share their points with you. Play farmers in fields that you can link to someone else's. But make sure you're not breaking the rules. As others have mentioned, it's kind of concerning that you had 7 meeples in a single field. You can't play on a feature someone else has already claimed. You have to add a meeple to a disconnected tile and then find a way to connect them.

In short, don't think of scoring as a single event when you finish a feature. Think of the value of every tile you lay as an immediate score. Moving your meeple on the scoreboard after the feature is complete is just a formality.