The old saying goes that practice makes perfect — and especially being that generally whenever you are welding you are going to need to make sure that the finished product meets a high level of standards, you want to get all the practice you can. Even the most experienced welders will encounter a challenge or two through the years and even if they can readily handle any obstacle in the way of a different material or unfamiliar order now, that probably wasn't the case in their earlier days. Having years of experience under their belts gives them the confidence they now have, but if you aren't quite there yet there are measures you can take to get well on your way and that means practice, practice, practice.
Yet at the same time you don't necessarily want to be practicing or testing your hand at a new technique on an important project or task, and while you are still learning you will most likely want to do this on a piece of scrap metal. These pieces of scrap sheet will work best if they are about 1.5mm thick for your first few go-a-rounds but you should then challenge yourself with a variety of thicknesses and you can usually get them from say a scrap bin at a welding fabricator that could sell them to you. Before you start you want to make sure that the metal is free of any paint or rust and is clean.
For an MIG welder you can get a steadier hand and better control by using both hands, so if you are just starting out and finding that one-handed approach just isn't cutting it you should make sure you have a good helmet that frees up both of your hands. When it comes to the tips' angle, shoot for about 20 degrees out of vertical and position the shroud forward. You want to practice getting the tip between 6mm and 10mm away from the metal, and a common mistake is holding it too far from the welding metal. This means your wire should be around 10mm in length and then allow the wire to graze the metal sheet. Work and test out a variety of different welding movements, and even though many will be roughly a zig-zag pattern you can make this motion a bit more curved to better work with pieces of metal that are thinner.
You will also want to work on your timing as a common mistake is moving too rapidly which will leave you with a weld that is both too thin and not adequate at joining the two pieces of metal. But move too slow and you'll be left with a hole in your sheet. Start by practicing on a single sheet and then work your way up to joining the two metals as you gain experience. You will also benefit from doing a sort of pushing motion when it comes to the direction in which you weld. You can make sure that you get the best coverage from shielding gas when you push rather than pull and should instill better habits now.
Keep up your practice with the MIG welder testing different thicknesses, movements, and then playing around with varying power settings. You may not be a pro welder yet but no one is on their first time out, no matter who says the opposite. Getting familiar with both the welder, how to hold it, how to most effectively work the tip, and all other aspects takes time and the more you spend at it the better you will be. Along with learning to weld comes patience, persistence, and of course practice!