I only make small batches because even if you put a lot of acidity in the dip the avocados will still turn brown after awhile. So unless you have a huge party that you are making this for keep the portions small.
I have also had a hard time finding just the right ripened avocados at the store so what I have started to do is plan ahead and pick up ones that aren't ripe yet and let them sit out on the table for a day or two at home. When ripe their skin will turn black and will just start to be soft to a light squeeze.
3 large Avocados (5 if they are small)
Onion - diced (I use red ones to give some color)
1/2 of a lime squeezed for juice
1 large Jalapeno - diced (leave the seeds if you want more heat)
Cilantro
Garlic - minced
Salt
Pepper
If you want more color you can also add some diced up roma or cherry tomatoes, they don't mess with the flavor much but add some nice color to the dip.
If you make this in advance only make it a few hours in advance and make sure it is sealed in an air tight container
Enjoy!