Spelling
If you've taught your child reading with a phonic method you'll find that he already has a head start when it comes to spelling because he already knows most of the common letter combinations. From about 7 (well, I'd say only if he's reading reasonably well and writing a bit, otherwise it won't mean much), you can start reinforcing and practising the GPCs he already knows from reading. (see Preparatory Level, English age 5-6 for an explanation of GPCs).
For the first stage, I tend to keep things simple and just give list of words with the same letter combination. So, I'll give my seven year old lists of 'ee' spelled words, then 'oa' spelled words etc. The next level is to give him mixed graphemes for the same sound. So, this time he'll get all the spellings for the 'ee' sound in the same list (such as 'ea', 'ee', e-e) or all the spellings for the long 'a' sound (such as ai, ay, a-e). Once you've gone through these, you'll have covered an awful lot of common words. Along the way you can add in all those common but 'tricky' words which don't follow the rules.
When the children are pretty secure in these letter combinations I just move onto a regular spelling book such as Schonell's Essential Spelling List. After all the grapheme practice, you'll find your child whizzes through the first few levels (in fact I tend to find mine are about a year ahead of their age-appropriate list).
One thing I've learned over the years (from reading books on a more 'Classical' approach) is the importance of explicitly setting out spelling rules - and reinforcing them. I used to think, 'We've covered the spelling rules' and move on, but I realise now that it's something some children need to keep revisiting (like basic arithmetic!). Here is a list of the 15 essential rules: Spelling rules. It's a good idea to make sure you know these by heart so you can re-inforce them regularly and explain why your child has misspelled a word.
Similarly, you may be ploughing through spelling lists yet find that your child misspells some very common words. It's a good idea to make sure the most common are very familiar. Here's one list; there are plenty to choose from (you can even find lists of the 1000 commonest words in English!)
In recent years, I've been using a British spelling course called Complete Graded Spelling Lists from Kit's Educational Publishing. There are two options: one book covering lists for Years 1-6, or three books covering Yrs 1-2, 3-4 and 5-6. The advantage of the latter is that each book contains not just lists but also interesting exercises to complement each word list.
With older children, when you've finished working through a standard text like Schonell's, it's a good idea to keep a list (or rather encourage them to keep a list) of words which are misspelled in any subject, and practice them until they are learned correctly. In fact, it's never too early to start this practice.