Here are some tips for your first games.
Fields of Green is an engine-building game. In order to do well, you must have multiple locations in your Farm working well together.
Essentially, what you need is to build some Fields which will convert Water to Food, then use your Livestock to convert Food to money and finally use that money to build Buildings that will grant you many points.
When drafting cards, don't look necessarily for the ones that list the most VP on them but look for what will make your engine more efficient. Also, try to keep track of your needs and make sure you don't overextend, building locations with Harvest costs you can't afford.
The more Fields you have, the more Water you will need. It is good to plan ahead for the Water you will be requiring and leave empty spaces where needed in order to build Water Towers there.
Also, Fields are usually more effective when they are built near each other since they can get water from the same Water Towers.
The decision of which cards to draw in the Upkeep Phase is more important than it may initially seem. The cards you choose determine the pool for that round so it allows you to affect what the other players will have access to in the draft.
Especially in 2-player games, the player going second has the advantage of being the one who ultimately decides how many cards of each type will be available in the round.