The Japanese verbs する (suru) and やる(yaru) are used quite frequently in the Japanese language, and while both of these mean “to do”, they have different usage.
Let’s start with two general rules to help distinguish between these two verbs.
First, する is more often used together with a noun to describe some action:
- 今晩、一緒に練習しましょう (konban, isshou ni renshuu shimashou)
- Let’s study tonight together.
- 僕は日本語を勉強しています。 (boku ha nihongo wo benkyou shite imasu).
- I am studying Japanese.
I have seen many onyomi (音読み, those whose pronunciation come from historical Chinese) used in this pattern, for example the two above (勉強、練習). However, kunyomi (訓読み) verbs can also be used with “suru”, for example “やり直しする” (yarinaoshi suru)
On the other hand, やる is often used on its own.
- あした、やることがある。 (ashita, yaru koto ga aru)
- Tomorrow, I have something to do.
- うまくやりなよ (umaku yari na yo)
- Do a good job! (literally something like to “Do it skillfully!”)
- 俺とやるか？ (ore to yaru ka)
- Want to fight with me?
The second rule is that generally やる has a ‘rougher’ feeling than する. For example:
- 何してるの？ (nani shiteru no?) [shiteru = shite iru]
- 何やってるの？ (nani yatteru no?) [yatteru = yatte iru]
- What are you doing?
Both of these basically mean the same thing, but the latter (yatteru) sounds a little more harsh to me.
There is one case where either verb can be used though, which is cooperative actions (共同動作), basically actions where several people are involved in a cooperative effort. For example, 試合 (shiai, “(sports) game”), 会議 (kaigi, “meeting”), etc.
- 来週、会議しましょう (raishuu kaigi shimashou)
- 来週、会議やりましょう (raishuu kaigi yarimashou)
- Let’s do a meeting next week.
Also, each of these verbs have separate meanings besides “to do”.
“Yaru” has another meaning which means “to give”, basically a rougher version of “あげる” (ageru). It is most often used to animals, children, or when you want to treat someone at a lower level than yourself.
- 犬に餌をやる (inu ni esa wo yaru)
- I will give food to the dog.
Also, just as “ageru” can be used after the “te” form to describing doing an action for someone’s sake (see this for details), “yaru” can be used in the same way.
- 勝たせてやるよ。 (katasete yaru yo).
- I’ll let you win.
“suru”, on the other hand, can be used in the special “~ ga suru” form to describe feeling something. See this page for more details and a few examples.
Make sure you don’t try to mix the words for these cases, for example “犬に餌をする” or “そんな気がやる” are incorrect.
This page has a more detailed explanation of these two verbs in Japanese.