Ateco #849 is perfect to make pretty swirls; this is a large nozzle that I use most of the time in all my frostings videos

Ateco #869 is a large French star nozzle that gives you that beautiful perfect swirl.

Wilton #1M and #1B are medium-sized nozzles that I use most often when I pipe roses on my cupcakes.

For piping bags, I love the brand sweet tooth fairy. 

Place your preferred piping tip/nozzle inside the bag, with the end snipped off so that the tip/nozzle fits through the hole. Just make sure that the bag does not cover the nozzle where the frosting comes out because it will block the frosting from coming out even on all sides.

I use an icing/frosting bag stand and place my piping bag in there. Spoon the frosting into the bag, filling half of the bag each time. Your beautiful hands are warm, and you do not want this frosting to melt on the last cupcakes, so it is better to fill the bag a few times instead of overfilling it.

Push the frosting down to the tip, squeezing out any air bubbles as needed. Twist the top of the bag slightly and proceed with piping.

The consistency of the frosting, the speed, and the pressure are very important when it comes to piping the perfect swirl or rose on a cupcake. All elements, if done well, create a full and even swirl or a beautiful rose. But at the same time, you have to do this at your own pace. You need to learn, have fun, and just do this with love.

I promise you the more practice you have, the better you will get at this.