According to the Duden (giving the standard of German language for German speaking countries) the imperfect is to be used if

1) an action that happened in a time before the one the event is talked about,
and
2) has no influence on the present time.

Gestern regnete es und heute scheint die Sonne. = Yesterday it rained and today the sun shines.

Actually the German rule (that nobody respects in spoken language) is the same as for the English imperfect. Only that in English language it has to be respected otherwise it sounds weird. In German everyone just accepts also the "wrong" version as right.

The rule for the present perfect according to the Duden is that Perfekt is to be used if

1) an action that started in a time before the one the event is talked about
and
2a) the action is finished and the result is still important in the present time
2b) the end of the action is in the present or even in the future

Heute hat es geregnet, aber jetzt scheint die Sonne. = Today it has rained, but now the sun is shining.

And here again it is the same as in English, only that the English use their rules and the Germans (against all prejudices) don't stick to their own rules.

Even though sometimes if the example is well chosen the difference might be noticed by a German:

Ich habe mein Geld verloren. = I have lost my money.

Unfortunately the money is gone and I didn't get it back yet. The result - that I don't have money - is still important to me.

Ich verlor mein Geld. = I lost my money.

The money is gone and maybe I got it back or not. Nobody knows, but actually it is not that important anymore. The thing I wanted to tell the other person was that the event of losing my money happened in the past.