I have done many Bargello quilts. One of the key ingredients to success is staying organized !! Do make a color key , make a strip set and cut a strip and mark each color in the strip with the correct number as it corresponds in the pattern. This is very important as you start the quilt. As you progress the pattern and colors will be come more apparent.
The second ingredient is take your time. It is a bit of a diffenrent process and will take some time getting your brain adjusted. One your brain is "re-trained" there is no stopping your level you are willing to take on. I continue to look for more an more "chanllenging" patterns.
I use a bulletin board to keep my strip sets and partial strips sets organized. I found this to be the most effective way to stay organized.
I wish you luck and know you will be hooked on Bargello.