Gemara

(Tana d'Vei Eliyahu): One who learns Halachos every day is a Ben Olam ha'Ba. We read "Halichos Olam Lo" like "Halachos". (The world to come is for him.)

Kidushin 30a (Rav Safra): "V'Shinantam (you will teach them) to your sons" - since it did not say "v'Shanisam", we expound this to say v'Shilashtam (you will divide in thirds);

One should divide his days in three. One third he should learn written Torah, one third Mishnah, and one third Gemara.

Sanhedrin 24a (R. Yochanan): "Bavel" alludes to the Talmud of Bavel, which is Balul (blended) with Mikra (written Torah), Mishnah, and Talmud.

Rishonim

Rambam (Hilchos Talmud Torah 1:11): One must divide his learning in three, and learn a third Mikra, a third Oral Torah, and a third Gemara. Gemara is understanding the end from the beginning, understanding one matter amidst another, comparing one matter to another and understanding the methods of expounding the Torah until he understands the essence of the Mitzvah and how the Isur and Heter result from teachings that he heard.

Rambam (12): This is at the beginning of one's learning. After one matures in Torah and he need not learn Mikra or engage constantly in oral Torah, he reads Mikra and teachings at regular intervals, lest he forget laws of Torah, and he fully focuses on Talmud, according to his ability.

Kesef Mishneh: Obviously, Gemara needs more time than Mikra and Mishnah. People rely on this not to divide the time in thirds.

Ran (Avodah Zarah 5b DH Ki): One divides the days of the week, and learns a third Mikra, a third Mishnah, and a third Talmud. I.e. he divides his time among them. He need not give equal amounts of time to each of them, for Gemara needs much time, and even Mishnah is harder than Mikra. He gives to each the time proper for it.

Tosfos (73a DH Tana): Some texts omit this ('anyone who learns Halachos...') It is in Rashi's text, and R. Tam amended his text to include it. It was included because the Gemara discussed a Halachah (a tradition from Moshe from Sinai), so it ends with a nice matter.

Maharsha (DH Tana): This teaching was brought at the end of Megilah, after R. Zeira's teaching that Benos Yisrael sit seven clean days even after a drop of blood. Kinim (obligations to bring birds for Korbanos) and Pischei (the start of) Nidah are Gufei (primary) Halachos; Tekufos and Gematriyos are accompaniments of Chachmah (Avos, Sof Perek 3). All of these involve great calculations and it is easy to err. However, an error in the latter would not cause problems. Even if Beis Din errs, their rulings (about a leap year or making the month 29 or 30 days) are valid. Therefore, this is not called Gufei Halachos. An error about Nidah (which can lead to Kinim) is likely to cause an Isur Kares. This is why R. Zeira's stringency was adopted! One might have thought that nowadays one need not learn Nidah, since R. Zeira's stringency fixes everything. Therefore, the Gemara teaches that whoever learns Halachos every day is a Ben Olam ha'Ba.

Tzitz Eliezer (12:93): We learn not only to know how to fulfill the Halachos. The learning itself enables one to merit the world to come. Therefore, there is no limit. One should learn Shas and repeat it his entire life. R. Nisim Ga'on (Sof Berachos) says that the exertion of learning brings Chachamim to continue to praise Hash-m and learn Torah also in the world to come.

Me'iri (DH Kol): 'One who learns Halachos' means that he investigates the Sugya thoroughly enough to decide the Halachah. He is guaranteed to be a Ben Olam ha'Ba, for through this his Hora'ah is proper. He benefits people through his rulings, and does not cause them to stumble, like Talmidim who do not learn so thoroughly.

Question: Reuven never learned Halachah with a Rebbi, and he does not know the ways of Halachah or its Perush or how to read it, but he has seen many Teshuvos of Ge'onim and Sifrei Dinim. There are mistakes in the copying of the Teshuvos, and perhaps the author later retracted. Can Reuven rule based on them in the same matter if he does not understand the matter, and from where in the Gemara we learn it, especially if he does not fear Shamayim and people have testified to his evil? They testified that one day he learned from one Gaon, and another day he attribute the same law to another Gaon.

Ri mi'Gash (114): Reuven is more qualified to rule than many who have established themselves to rule, even though they do not understand the Halachah or the Ge'onim. We should stop those who seek to rule based on their investigation of the Halachah and the Talmud, for nowadays no one is qualified to do so without knowing the Ge'onim's opinion. One who rules based on Teshuvos ha'Ge'onim, even though he does not understand the Talmud, is more proper to rule than one who thinks that he understands the Talmud and relies on himself. Even if the former rules based on improper reasoning from proofs of the Ge'onim, he does not err, for he rules based on a great expert Beis Din. The latter is prone to err because he explained incorrectly. I have seen rulings of people who think that the Halachah is clear, and they learned from a place from which we cannot learn. They do not make fine distinctions. However, if a judge lacks Yir'as Shamayim, appointing him is like planting an Asherah (a tree for idolatry) in Yisrael.

Poskim

Shulchan Aruch (YD 246:4): One must divide his learning in three, and learn a third Mikra, a third Mishnah, i.e. Oral Torah, which includes explanations of the Torah, and a third Talmud. Talmud is understanding the end from the beginning, one matter amidst another, comparing one matter to another and judging based on the methods of expounding the Torah until he understands the essence of the Mitzvah and how the Isur and Heter result, and traditions. After one matures in Torah, it suffices to have set times to read Torah, Nevi'im and Kesuvim and Oral Torah, lest he forget laws of Torah, and he fully focuses on Talmud.

Rema (YD 246:4): Some say that Talmud Bavli is mixed with all three of these, so one is Yotzei everything through it. One should learn only Mikra, Mishnah, Gemara and Poskim based on them. Through this one acquires this world and the next. One should not learn other Chachmos.

Drishah (2, brought in Taz 2 and Shach 5): Some Ba'alei Batim learn every day Gemara, Rashi and Tosfos, but not other Poskim. They bring a proof from Nidah, which says that one who learns Halachos every day is a Ben Olam ha'Ba. I disagree. Rather, one should know the laws of the Torah through Poskim such as the Rif, Mordechai, and Rosh. This is the source of Hora'ah (Halachic rulings). One is not Yotzei through mere Gemara, Rashi and Tosfos. Rashi explains 'one who learns Halachos...' refers to clearcut Halachos. R. Tam says that the Bavli includes a mixture of all three, i.e. for one who has nine hours a day to learn. Since he has much time, he should learn Talmud. Ba'alei Batim who learn only three or four hours a day should not learn only Talmud.

Mishnah Berurah (155:3): Every day, one must learn Mikra, Mishnah, Gemara and Poskim. Ba'alei Batim who learn only three or four hours a day should not learn only Talmud, for then they are not Yotzei. Rather, they should learn also Poskim, everyone according to his ability.

Yechaveh Da'as (6:52): Ya'aros Devash says that one who has not learned Hilchos Shabbos clearly two or three times cannot avoid transgressing Shabbos, mid'Oraisa and mid'Rabanan. Derech ha'Chayim (114b) and Kaf ha'Chayim (Palagi 29:3,9) add that some people outstanding in Pilpul (deep investigations in Torah) are not fluent in Hilchos Shabbos at all, and they come to Safek Chilul Shabbos. Learning Gemara and Rishonim is not so valuable if he does not conclude the Sugya according to the Halachah, like the Shulchan Aruch and Acharonim, in laws that apply often. If one learns Daf Yomi, and at the same a qualified Moreh Hora'ah teaches Halachah, the latter is better, so he will know what is permitted and forbidden, and practical Halachah, and not stumble in Chilul Shabbos, Berachah l'Vatalah, etc. A mistake in learning is considered Mezid. One who fears Shamayim will fulfill both, if he can learn both Daf ha'Yomi and Halachah from a Posek. One may cease learning Daf ha'Yomi in order to learn practical Halachah, and he need not permit his vow.