Counting things and also matching them are the main things to start with. When you count, remember to alter your voice on the last number as you speak - "one, two thREE.!" as it is very important that the children pick up not only the sequence of words, but also the fact that it is the last number that matters. - Ie that four objects are not just 'one, two, three, four' but we describe them as 'four' things. (Most children get this easily, but there are always a couple who don't pick it up and it can cause problems later on as the confusion they experience puts them of maths.)
Put things in groups by their shape or colour and count the numbers in each group. Ask how many pieces are missing in the jigsaw when they have nearly finished.
Feet and hands are wonderful resources, as are counting rhymes and songs. Match shoes and feet and talk about pairs and counting in 2s. Make five-petalled flowers by dipping finger tips in paint and holding them together and dabbing on the paper and then drawing a stalk. Talk about 1 stalk and 5 petals and integrate this with exploring outside and looking at real flowers and seeing how many petals or leaves they have etc. Talk about the differences between the things you see.
Ask questions of the children and help them answer - 'How many chairs/ apples/mugs do we need today. Let's count them together. Oh dear! Dan hasn't a mug. There are only _ mugs. We need one more. We need _ . Let's get another one for Dan to make _.
Then make sure you do weighing - making cakes etc, measuring - who is tallest, which is the biggest teddy bear etc. Try to use as any different words as possible for these concepts - smaller, taller, bigger, larger, tiny, less than, wider, fatter, longer, shorter, shrink, grow, more than,difference, etc. Try to have at least 2 things to compare as often as possible.
They need to learn the shape of the figures as well as their names. Colouring sheets with, for example, a big number 5 in outline and 5 teddy bears to colour, for instance are good. You can praise the colouring and count the bears together and talk about the shape of the number.
Well, that's a few! I could go on!
Years of experience