For れば (すれば,　食べれば　etc） I think one of most common usages I have heard is the 。。。すればいい structure. It is used when suggesting that it would be a good idea to do something, or it can also sound kind of like an order depending on the tone. As in もっと勉強すればいいだろう。 れば also has heaps of other usages as well though. This is the closest conditional to 'if' in English imo. 明るいところで本を読めば、目は悪くならないよ。 寒ければ、窓を閉めてく下さい。 お茶をおいしく作れば、永住権を取れる。(Just in case you want to live in Japan) Also と I mentioned earlier is useful 私のアパートは、夏になると、とても暑い。（like when) 勉強すると、。。。　When I study。。。 You can't use it like this however. 来年、日本に行くと...　When I go to Japan next year... Maybe use たら for this situation? Sorry I can't give you any specific rules and can't tell you the specific difference between the conditionals. Some textbooks do have rules written, but there are always sentences that don't fit to these rules, exceptions and so on... No Japanese seem to know how the conditionals work, they just know how to use them because they have grown up speaking Japanese. Good luck anyway, hope I could help.

Conditionals... one of the hardest things to learn to use naturally in Japanese. lol Unfortunately there aren't any simple rules that say when each one is ok to use, and in many situations you can use more than one. If you are going to study them you might as well learn the other conditional と　at the same time. たら is used for if/when something happens. 太郎さんが行ったら、私も行きます。 The first part has to come before the second part 太郎さんの家へ行ったら、前もって電話します。　WRONG 太郎が来たら、ジョンが帰った。　OK The following are not ok: 太郎が来たら、僕が帰った。　WRONG 昨日、ご飯を食べたら、テレビを見ました　WRONG 布団に入ったら、すぐ眠ってしまった　This is ok. If the sentence is in the past, the second part has to be non-controllable. (the last one is ok I guess because you can't 'control' when you fall asleep) Ok, now なら。(するなら、行くなら　etc)　　Conditionals are difficult to explain. The best way is just to listen to Japanese speaking and listen to which conditional they use and where they use it. I'll just give you some examples. あなたが行くなら、僕もいっしょに行こう。　OK ジョンが来たなら、ボブさんは帰った　NO 日本語を話すなら、正しい日本語を使いましょう。　OK 日本語を話すなら、スミスさんには分からない。　NO Don't ask my why you can't use those ones I put no for, they just sound weird.

It's just my opinion, so it might be wrong from grammatical point of view, but I think this make sense. ーしたら　is usually used in conversation. Then, ーするなら is also used in conversation. but ーしたら has a meaning of "assumption" and ーするなら　doesn't have that meaning. ーすれば can be used for both meaning, and it's not wierd if you use that in sentences.