The first part of any gumbo is the roux. If you don’t start with a good roux you won’t get a good gumbo.
To make the roux:
Heat the pot on medium heat. Add the oil and warm it. Add the flour, stirring to blend it with the oil. You can use a whisk for this part but
When it gets to that point you add:
add:
a pound (or more) of good spicy (hot preferred) smoked sausage like andouille or kielbasa or even Italian sausage, cut into bitesize pieces
a half pound (or more) of Tasso or spiced ham or even regular ham (just not the too salty kind) cut into small cubes
stir it all well and cook for another 4 or 5 minutes.
Then add 3 quarts of chicken stock (I make homemade a lot but canned soup or bouillon cubes works too just cut way down on the other salt in the recipe) that is cooled to room temperature to the roux mixture. Stir well to combine it. Bring it to a boil, then reduce heat to medium or low, stirring it every 5 minutes or so, for at LEAST an hour. You cannot rush good gumbo.
Add 3 cups of cooked chicken meat (I use a whole chicken to make the chicken stock and this is where I get the meat from but you could just boil or steam a couple chicken breasts and add them instead)
Stir thoroughly and let the chicken heat through.
Add as much shelled de-veined shrimps as you like/can afford, and let cook through til the shrimps are all deep pink
Taste the seasonings and adjust if needed (gumbo should be spicy but not take off your head)
Take it off the heat and stir in about 2 TBSP chopped parsley and 1/2 C of chopped green onions (the green and white parts)
Ladle into deep bowls, add a big scoop of rice into the middle of each bowl, and (if you like it) sprinkle with file' powder.
continue to stir for 4 or 5 minutes until the onions start to look wilted a bit.