But after a time that becomes a bit boring. So you can add some up-strokes.
1 2 and 3 4 and 1 2 and 3 4 and … …
There are also songs in ¾ or 6/8 time signature. You can change between up- and down-strokes like this:
1 2 3 1 2 3 … …
Keep your right hand relaxed! You don't have to move your forearm up and down – it's better to move your hand up and down by a relaxed rotation of your wrist!