Following a melody is a good idea, but also creating a counter melody, that goes with all the chord progressions, is a really fresh thing to do. It will compliment whatever the vocalist is singing.
The 4 and the 6 of the chord are the hardest - they typically only work on certain chords. The 1, 3, 5 and 2 work on almost anything. This is something you learn via trial and error and is determined by what sounds good to the ear.
A lot of times you don’t even need to change the notes, just change up the order in which they are played. The bass guitar and the keys can be playing two totally different progressions and it can still work. The most important thing is that the harmonies are complementary to each other.
the dynamic between ascending and descending patterns.
Octaves are another great way to add some variety in your sound
a latch-pad underneath
adding quarter notes
Listen to the vocalist and decide if what you’re wanting to play is going to compliment them. Don’t use sounds that will distract from the worship leader.
You will want to have a lot of tools available to you. Try to get a good 4–8 sounds/textures that will allow you to rise and fall throughout a song as needed.
Step back and look at the overall picture of what your worship band is doing - do you compliment them?