Artwork

For Lithography printing a bleed should be used to avoid having a white edge of unprinted stock. Bleeds are usually 3mm but it is always best to discuss with your printers first.

Bleed - The printing of a design over and beyond its trim marks

Trim - The process of cutting away the waste stock around a design to form the final format once the job has been printed. 

Registration - The exact alignment of two or more printed mages with each other on the same stock

Types of Black
Four Colour Black - It is the darkest black and is produced by overprinting the 4 process colours. This may cause issues with ink drying and smudging.

Rich Black - A practical solution to 'bounce', a registration problem that can occur when an area of no colour is adjacent to an area of heavy coverage. Printing with a 50% shiner of cyan, magenta and yellow produces a grey colour that covers any registration errors with the black because the image now has shared colours.

Registration Black - It is a black obtained from using 100% coverage of the four process colours, using registration colour for text and greyscale graphics is a common error and gives an undesirable effect. 

Warm & Cool blacks - Flat areas of black can be enhanced by applying a shiner of another colour underneath

Registration Problems - (This is more the printers responsibility) A 4 colour image will look distorted or blurred if the plates are not aligned properly. This isn't an issue with a single colour print job.

Trapping

Sometimes gaps can appear between the different sections of colour, this can be resolved using trapping, a process where one printed ink is surrounded by another that effectively traps it.

The main options that are used for trapping are choke, spread and centre trapping. They are all set up with automatic features but these can be increased and decreased respectively.

Spreading - Where the lighter object is made larger to spread into another darker one

Choke - Used to reduce the size of the aperture that an object will print in

Centred trapping - uses a combination of enlarging the object and reducing the aperture by the same amount.

Over Print - When one colour prints over another. (left image) - Industry example
Knockout Print - Where a gap is left in one colour for another colour to print in (right image)
Reverse out - When instead of the design being printed it is removed from a block of printed colour and left as an unprinted area.
Surprint - Describes two elements that are printed on top of one another and are tints or the same colour. I.e. Text on