The form of verb is different, but the meaning is almost the same! もしわたしが走ったら もしわたしがはしるなら As you can see, you have to use "て-form" (my friends call it so) in the もし たら sentences. In the もし なら sentences, you have to use plain form. "もし なら" sentences indicate that the person will do something in the future. "もし たら" sentences sound like it is more assumption-like thing. Does it make sence? haha~

I noticed more differences. So I add them. 5. たらcan be used in advise by itself. もっと勉強し［たら］？（correct）Why don't you study harder? / You should study harder. もっと勉強する［なら］？（incorrect） 6. The assumption of ［なら］is stronger than the one of ［たら］. 頑張<がんば>っ［たら］できます。（correct）If you do your best, you will be able to do it. 頑張<がんば>る［なら］できます。（correct）If you do your best, you will be able to do it（I don't know whether you will do your best）.

An assumption particleたらis an abbreviation of たらば. ば is a conjunction particle express an assumption. たら was originally a conjugation of たり(an old auxiliary verb to express completion). So it is used as "When＝at the time that it has finished" or "If＝After the assumption would be realized ". An assumption particleならis an abbreviation of ならば. なら was originally a conjugation of なり(an old auxiliary verb to express conclusion). So it is used as " If＝in the case the fact would be changed ". 1.ならcannot be used in "found a new situation". 私<わたし>が窓<まど>を開<あ>け［たら］、目<め>の前<まえ>に紺碧<こんぺき>の海<うみ>が広<ひろ>がりました。（correct）　When I opened the window, the dark blue sea spread out at hand. 私が窓を開ける［なら］、目の前に紺碧の海が広がりました。（incorrect） 2. ならcannot be used about "what you do not need to assume". 5時<じ>になっ［たら］帰<かえ>ります。I'll go back at 5(o'clock). （correct） 5時になる［なら］帰ります。（incorrect） 3. たらcannot be used in advise. 日本語を勉強したらitalkiがいいですよ。（incorrect） 日本語を勉強するならitalkiがいいですよ。（correct）If you want to learn Japanese (language) , italki is good. 4. The next phrase of たら is the thing after the former thing finished and the next phrase of なら is opposite. 飲ん［だら］乗るな。When you've drunk, don't drive (a car). （correct） 乗る［なら］飲むな。If you drive (a car), don't drink (alcohol). （correct）

how about negative verbs