Summarize:

Look for a compound that you mix at home, rather than one that is pre-mixed. If you can’t find a powdered compound, just go with a pre-mixed one. Talk to the store clerk about using a brand that is smooth and hardens fast.  There are a couple of key advantages to using a mix-at-home compound. Firstly, it hardens much faster than pre-mixed compound, and secondly, it doesn’t shrink once it dries, unlike pre-mixed. The amount that you will need obviously varies depending on the size of your job, so talk to the store assistant about how much they recommend you buy for the space you are working with. In this situation, it’s better to have too much than too little. This tool is the most important of all the tools you will use for this project. Getting a larger knife (there are also 6 in (15 cm) knives available) allows you to apply more compound at once. Make sure you find an actual drywall knife, rather than a multi-purpose tool You use a drywall knife to apply the compound to the drywall. You also use it to smooth out and remove excess compound after the initial application you put down. Look for mesh tape that is specifically for use on drywall. You can find this tape at most home goods stores and it is fairly cheap to buy. Talk to the store clerk about what specific brand might be better for your particular needs.  Mesh tape is much easier to use than paper tape. Paper tape has some advantages, such as being a little bit stronger, but for a novice plasterer, mesh tape is a much more straightforward option to deal with. Mesh tape goes down over any joins between pieces of drywall. It provides the base over which you start applying the ‘floating’ compound. Look for a sanding sponge of about 180 grit. If you can’t find a sanding sponge, just get sandpaper. Sanding sponges are great for more heavy duty jobs because of how easy they are to hold and use.  You use a sanding sponge to smooth out the compound mix once it has eventually hardened. Buy the best quality sanding sponge you can afford, as sometimes the cheaper ones can deteriorate fairly quickly after some heavy use.
Find a high-quality lightweight joining compound. Get hold of a 10 in (25 cm) drywall knife. Buy some mesh tape to lay down first. Purchase a high-quality sanding sponge.