The basic tools.
Tweezers are a tool that no modeler can do without. It is needed to hold any small piece where your fingers are to big or can't reach. They come in many sizes and styles. There are straight, angled, reverse and wide. They all have a similar purpose but have different uses. The straight tweezers can come in different lengths, but I prefer the longer ones as they allow for further reach. The angled tweezers allow you to hold pieces in place where straight tweezers just won't reach. I like the reverse tweezers for holding decals as the sit in water. The wide tweezers are good for positioning the decals as it allows you to hold more of the decal without destroying it.
A hobby knife is also a must have tool as it allows you to remove the pieces from the sheets without destroying them. It is also good for removing any unwanted bits from the pieces so they look like their supposed to. It is also a good tool to use if you glue a piece in the wrong spot or need to remove some plastic to create a hole. A good quality Stanly knife is better then a hobby knife as the blades are a little stronger and more force can be applied.
The advanced tools.
These tools are not required to complete a model but make building that perfect model a little easier. They are tools like side cutters, files, magnified glass steel ruler and clamps.
Files can be used to create that perfect piece and remove the last of the unwanted plastic that is used in the molding process. Files can come in many different sizes and roughness, I like to have a rough and a fine file and also a skinny and round file. The different files allow you to get into tight curves and the fine files allow you to get the last little bit of unwanted plastic off. You can also have a half round file for that one curved piece that needs a little taken off.
Side cutters are a great tool to have to remove the pieces from the sheets to avoid breaking them. They are also good for removing excess plastic that would take a while with a file. A good quality pair is not necessary as you're only cutting plastic and it is fairly easy to cut through.
A magnifier is a handy tool to have when painting small parts or painting two colours near each other. It allows you to get a closer look at where your painting to achieve that perfect paint job. A handy magnifier with a stand is a good idea as it allows you to have both hands free to hold tools and your model. A head band with magnifier is a good option as it allows you to move the magnifier or piece to exactly where you need it.
Clamps are a great tool to have to hold pieces together while the glue is drying. A quick clamp that is able to be used by one hand is easier, you can hold onto your pieces with one hand and use the clamp with the other. A g style clamp is good for those wide pieces and a c clamp is good for most pieces you need to clamp.
A steel ruler can come in handy when you need to start putting on the decals. It is handy when cutting the decals from the sheet to avoid destroying any. I use either a small 150mm ruler or a long 300mm ruler depending on what size the decal is.
You won't need to buy all these tools when you start modeling, you can buy them as you need them. I have bought these tools over time when I needed them and have spread the cost over time.
It is handy to have a place to store all your tools. A tool box is handy but it is a good idea to keep it organised so you can find the right tool when you need it. I have a large tool box that is fool to the brim, I might need to get a bigger tool box or even a wheeled box.