merry meet. there are plenty of books and articles to help you get started, but being able to focus on one thing is rather important in spell casting. hopefully this article can provide some insight:
meditation is important but it can take people a long time to get. when i started i would repeat the word 'one' in my head [my grandmother told me to] and it worked. some people tend to focus on positive words like 'peace' or 'joy' some simple thing to calm their mind breathing is another thing people focus on, they may also listen to a clock or metronome, music, white noises, and so on to help them. along with sound, some people will use tea, oils, or incense to help them get into a relaxed state. there are many options, try a new method each week until you discover one that's right for you. there is also many forms of meditation, many think to meditate you need to clear your mind and do so for hours. there are other forms, as long as you relax and don't give into random thoughts you're fine. aim for a minute in this state, then slowly work your way up.
regarding books, whats your path? or do you just want spell work? some paths will or won't cast certain spells, or use certain items. there's also the question of who you're directing the spell to? is it a particular deity or the universe? anyway, good luck on your path, blessed be.