Write - your children should see you writing all the time. Whether it's notes to your partner, typing your blog (C is watching me right now), writing a shopping list, writing letters, labelling pictures, writing in a diary, journal or calendar or just noting your ideas. If you usually use your i-pad to make notes and lists then that's fine some of the time, but try to use paper and pencil too.
Ensure that your child has access to pencils, pens and paper. Notebooks, old diaries and calendars, shopping list pads, pads of paper, different types of pen, pencil, highlighter, eraser and so on. Your child will want to make marks on the paper, and if they see you writing with a purpose, then they'll start to incorporate that into their play, writing notes and letters all over the place. C (age 4) has made a joke book quite recently and Bug (aged 2) is regularly writing birthday cards to her teddy. Praise all attempts at marks that are supposed to be writing, and point out the marks that look like letters, your child will want to repeat those ones.
When introducing letters, use tactile ones and encourage your child to trace over the shape of the letter with their finger. Also play lots of games and activities introducing letter shapes, such as letter printing, making letter shapes with playdough or plasticene, sticking letter shapes, drawing letter shapes in salt or sand trays.
Provide an easel, chalk board or white board for lots more mark making fun.
Encourage your child to copy you drawing vertical (standing up) lines, horizontal (lying down) lines, circles, wave patterns and zig-zag patterns. Also encourage them to trace over your lines, shapes and patterns.
Begin to introduce letter formation. You can buy early handwriting books from supermarkets and book shops. Some use dry-wipe pens so that they are wipe clean. Most will start with simple pattern tracing, and build up to similar groups of letters. Always do these with your child so that you can help them to hold the pencil correctly and to start the letters in the right place. Poor habits started now will be difficult for your child's teacher to fix later. It's very important not to push this. If your child struggles to trace over the lines then leave it, go back and do more activities to develop hand-eye co-ordination and come back to the early handwriting a couple of months down the line. If your child has had enough after tracing four letters, then let them stop and come back to it when they are ready. You can get special left-handed handwriting books from www.anythinglefthanded.co.uk which offer handy hints on letter formation and page orientation for left-handers.
Make a name card for your child using cereal box card and clear writing, and then make a tracing paper booklet the same size. Get your child to practice tracing over their name (naming the letters/sounds as they go) until they can do this confidently without the tracing. From this point on, always get your child to write their own name on birthday and Christmas cards and on their art work.
Once your child is confidently reading CVC words (consonant-vowel-consonant words such as cat, mug etc) and can confidently form most of their letters, then encourage them to write a word and draw a picture to accompany it.
Continue developing neat letter formation by getting your child to dictate a sentence, which you write in, for example, a daily diary, using yellow felt pen or orange pencil and getting your child to trace over it and then draw an accompanying picture. You can begin to get your child to sound out the words for you to decide which letters should be used. Once they are confident with this, you can start to get them to write their own simple sentences.
Where do I get the ideas and information from? I'm an experienced primary school teacher, and also a mother of two (aged 4 1/2 and 2 1/2). Bug, the younger, is at the stage where she tells me she is writing, and some of her marks are beginning to resemble letter shapes. C is much more confident, can write his name with ease, as well as other CVC words, and attempts on others. He dictates and traces a sentence at least once a week in his daily diary.