Use fresh parsley! It really added a nice freshness to the compound butter that was worth the added effort it took to chop the parsley.
Don't skimp on the lemon zest. It was a last minute decision to add the zest too and it was so worth it!
Don't "melt" the butter before mixing. If your butter is too cold to mix with the other ingredients, you can put it in the microwave but do so sparingly. I put it in for 5-10 seconds and check it in between microwaving times. You do not want melted butter, you want soft butter. If you do accidentally melt it (I admit that I have done it), it's not the end of the world. After all ingredients have been combined, stick it in the freezer for 5 or 10 minutes and then stir well. You want to make sure that you get all of the butter recombined. If you don't stir it well before using, you will have portions that have all of the the fat and salt (and flavor) and other portions that are more oily tasting.