Aphids can be such pests! While it seems like every succulent grower I know has had to deal with them at one point or another, getting rid of them is not too difficult.
One of the best ways is to use 70% isopropyl alcohol and spray it on your plants, just as you would a mealybug infestation. Don’t be discouraged if you have to apply this more than once.
You can also add a tiny bit of dish soap to an isopropyl alcohol and water solution; this emulsifies the mix, making it stick to your plants better.
If you need a bit of a stronger approach, you can also spray your plants with insecticidal soap.
To prevent aphids from being drawn to your plant in the future, be sure your succulents are in well-draining soil, and that you are letting your soil dry out completely between watering. It’s also important not to reuse your soil after repotting. This will help prevent eggs from any pest spreading into your new pot.