Kitzur Shulchan Arukh 151:5

אָסוּר לְהוֹצִיא זֶרַע לְבַטָלָה. וְעָוֹן זֶה חָמוּר מִכָּל עֲבֵרוֹת שֶׁבַּתּוֹרָה. וְאֵלּוּ שֶׁמְּנָאֲפִים בַּיָּד וּמוֹצִיאִים זֶרַע לְבַטָּלָה, לֹא דַי לָהֶם שֶׁאִסּוּר גָּדוֹל הוּא, אֶלָּא שֶהָעוֹשֶׂה זֹאת, הוּא בְנִדּוּי, וַעֲלֵיהֶם נֶאֱמַר, יְדֵיכֶם דָּמִים מָלֵאוּ, וּכְאִילּוּ הוֹרֵג אֶת הַנֶּפֶשׁ. וּרְאֵה מַה שֶּכָּתַב רַֹשִ"י בְּפָרָשַת וַיֵֹשֶב בְּעֵר וְאוֹנָן שֶׁמֵּתוּ בְּחֵטְא זֶה. וְלִפְעָמִים בְּעֹנֶשׁ זֶה, חַס וְשָׁלוֹם, בָּנָיו מֵתִים כְּשֶׁהֵם קְטַנִים, אוֹ שֶׁיִהְיוּ רְשָׁעִים, וְהוּא בָא לִידֵי עֲנִיוּת. It is forbidden to discharge semen in vain. This is a graver sin than any other in the Torah.¹Zohar, Shulchan Aruch, Even Ha’Ezer 23:1. Beis Shmuel explains this is not meant to be taken literally. Any sin that carries a penalty of death or koreis is a graver sin. This is meant to impress man with the severity of this sin. Those who masturbate and thus discharge semen in vain, not only do they commit a grave sin, but also one who does this is placed under a ban. Concerning such people it is said, "Your hands are full of blood,"²Isaiah 1:15. and it is likened to killing a person. See what Rashi wrote in the Sidrah of Vayeishev³Genesis 38:7. concerning Er and Onan, who died because of committing this sin. Occasionally, as a punishment for this sin, God forbid, one's children die when young,⁴Under the age of Bar or Bas-Mitzvah. or grow up to be wicked, while the sinner is reduced to poverty.

אָסוּר לְאָדָם שֶׁיְקַשֶּׁה אֶת עַצְמוֹ לָדַעַת, אוֹ שֶׁיָבִיא אֶת עַצְמוֹ לִידֵי הִרִהוּר אִשָׁה. וְאִם בָּא לוֹ אֵיזֶה הִרְהוּר, יַסִּיעַ אֶת לִבּוֹ מִדִּבְרֵי הֲבַאִי לְדִבְרֵי תוֹרָה, שֶׁהִיא אַיֶלֶת אֲהָבִים וְיַעֲלַת חֵן. וְאֵין מַחְשֶׁבֶת עֲרָיוֹת מִתְגַּבֶּרֶת אֶלָּא בְּלֵב פָּנוּי מִן הַחָכְמָה. וְיִזָּהֵר מְאֹד שֶׁלֹּא יָבוֹא לִידֵי קִשּׁוּי. לְפִיכָךְ אָסור לְאָדָם לִישֹׁן עַל עָרְפּוֹ וְפָנָיו לְמַעְלָה, אוֹ לִישֹׁן וּפָנָיו לְמַטָה, אֶלָּא יִישַׁן עַל הַצְדָדִין, שֶׁלֹּא יָבוֹא לִידֵי קִשּׁוּי. וְלֹא יִישְׁנוּ שְנֵי רַוָּקִים יָחַד. וְלֹא יִסְתַּכֵּל בְּבְהֵמָה חַיָה וָעוֹף כְּשֶׁמִּזְדַּקְּקִין זָכָר לִנְקֵבָה. וְאָסוּר לִרְכֹּב עַל בְּהֵמָה בְּלֹא אֻכָּף. It is forbidden to bring on an erection (in vain), or to cause yourself to think about women. If a [lewd] thought comes spontaneously, you should divert your attention from nonsense to words of Torah, which is likened to, "A lovely hind and a graceful doe." Lewd thoughts prevail only in a heart devoid of (Torah) wisdom. You should be extremely careful to avoid an erection. Therefore, it is forbidden to sleep on your back facing upward, or to sleep (on your stomach) facing downward, but you should sleep on your side to avoid an erection. Two bachelors should not sleep in one bed. You should not watch animals, beasts, or fowl when the male and female copulate. It is forbidden to ride on an animal without a saddle.

כְּשֶׁמַּשְׁתִּין, אָסוּר לֶאֱחֹז בַּמִּילָה לְהַשְּׁתִּין. וְאִם הוּא נָשׂוּי וְאִשְׁתּוֹ עִמּוֹ בָּעִיר וְהִיא טְהוֹרָה, מִצַּד הַדִּין מֻתָּר לוֹ, דְּכֵיוָן שֶׁיֵשׁ לוֹ פַּת בְּסַלּוֹ, אֵינוֹ בָא לִידֵי הִרְהוּר וְחִמּוּם. אַךְ מִמִּידַת חֲסִידוּת, לְהַחְמִיר. וְשֶׁלֹּא לְצֹרֶךְ הַשְׁתָּנָה, גַּם מִצַּד הַדִּין אָסוּר לו. When urinating, it is forbidden to hold the penis⁵From the glans and downward is permitted even while erect. (Mishnah Berurah 3:25) even to facilitate urination. If you are married and your wife is also with you in town, and she is clean (menstrually), from the halachic standpoint it is permitted; for when a person has the possibility, he will usually not succumb to lustful thoughts and stimulation. But it is a matter of piety to be stringent even in this situation.⁶If you are standing in a place where you are afraid of falling, it is not even piety to be strict, provided you are married. (Mishnah Berurah 3:28) When not for the purpose of urinating, even halachically the above mentioned things are forbidden.

בִּסְעוּדַת הַלַּיְלָה, לֹא יַרְבֶּה בַאֲכִילָה וּבִשְׁתִיָה, וְלֹא יֹאכַל דְּבָרִים הַמְחַמְּמִים אֶת הַגוּף, כְּגוֹן בָּשָׂר שָׁמֵן וְכָל מַאַכְלֵי חָלָב וּגְבִינָה וּבֵיצִים וָשׁוּם. גַּם לֹא יִשְׁתֶּה מַשְׁקֶה הַמְחַמֵם, כִּי דְבָרִים אֵלּוּ גּוֹרְמִים לְחֵטְא זֶה. At supper you should not eat or drink excessively nor eat any foods that tend to heat the body, such as fat meats, all milk products, cheese, eggs, and garlic. Neither should you drink a beverage that tends to heat the body, for these things cause the committing of this sin.

הָרוֹצֶה לִשְׁמֹר אֶת עַצְמוֹ מֵחֵטְא זֶה, יִשְׁמֹר אֶת פִּיו מִנִּבּוּל פֶּה, מִשְּׁקָרִים, מֵרְכִילוּת וּמִלָּשׁוֹן הָרַע וּמִלֵּצָנוּת. וְכֵן יִשְׁמֹר אֶת אָזְנוֹ מִשְּׁמֹעַ דְּבָרִים כָּאֵלּוּ. גַּם יְהֵא זָהִיר לְקַיֵם נְדָרָיו, וְלֹא יַרְבֶּה בִּדְאָגָה, וְגַם יְהֵא זָהִיר מֵהִרְהוּרִים רָעִים. וְקֹדֶם שֶׁהוֹלֵךְ לִישֹׁן, יעֲסֹק בַּתּוֹרָה, אוֹ יֹאמַר אַרְבָּעָה מִזְמוֹרֵי תְהִלִּים הָרִאשׁוֹנִים (עַיֵן לְעֵיל סִימָן קלב סָעִיף ה), וְיִזָּהֵר שֶלֹּא לִישֹׁן בַּחֶדֶר יְחִידִי. If you wish to avoid this sin, guard your mouth against obscene language, lies, talebearing, slander, and mockery. You should also guard your ears from hearing such talk. You must also be careful to fulfill your vows, not to worry too much about things, and be careful to guard yourself against lewd thoughts. Before going to sleep you should study Torah or say the first four Chapters of the Psalms,⁷See Kitzur Shulchan Aruch 132:5. and be careful not to sleep alone in a room.

תִּקּוּנִים לְמִי שֶׁנִּכְשַׁל בְּחֵטְא זֶה כְּתוּבִים בְּסֵפֶר יְסוֹד יוֹסֵף, אֲשֶׁר לִקֵּט וְאָסַף מִסְּפָרִים קְדוֹשִים וְקַדְמוֹנִים. וְאֶכְתֹּב פֹּה קְצָת מֵהֶם בְּקִצּוּר, לְהַדֵּר לִהְיוֹת סַנְדָּק, שֶיִמּוֹלוּ יְלָדִים עַל בִּרְכָּיו, וּבִפְרָט לִהְיוֹת סַנְדָּק אֵצֶל עֲנִיִים, לְהַרְבּוֹת בִּצְדָקָה לַעֲנִיִּים, לִשְׁמֹר שַׁבָּת כְּהִלְכָתָהּ וּלְעַנְּגָהּ וּלְהַדְלִיק נֵרוֹת הַרְבֵּה, לְכַבֵּד וְלֶאֱהֹב לוֹמְדֵי תוֹרָה, לְהִתְפַּלֵּל בְכַוָּנָה וּבְבֶכִי, לִבְחוֹר בְמִדַת הָעֲנָוָה. וְכַאֲשֶׁר יִשְׁמַע שֶׁמְּחָרְפִים אוֹתוֹ, יִשְׁתֹּק וְיִמְחֹל. כַּאֲשֶׁר יַעֲשֶׂה אֵיזוֹ מִצְוָה, יַעֲשֶׂהָ בְכֹחַ וּבִזְרִיזוּת עַד שֶׁיִתְחַמֵם בָּהּ, וּבִפְרָט בַּעֲשִֹיַת הַמַּצּוֹת לְפֶּסַח. לְגַדֵּל בָּנָיו לְתַלְמוּד תּוֹרָה וּלְהַדְרִיכָם בְּיִרְאַת שָׁמָיִם. לְגַדֵּל יָתוֹם בְּתוֹךְ בֵּיתוֹ, וְיִתְנַהֵג עִמּוֹ כְּמוֹ עִם בְּנוֹ. לַעֲסֹק בְּמִצְוַת הַכְנָסַת כַּלָה. לַעֲלוֹת לַתּוֹרָה לְכָל הַפָּחוֹת פַּעַם אַחַת בְכָל חֹדֶשׁ, וִיבָרֵךְ הַבְּרָכוֹת בְּקוֹל רָם. גַם יִסְתַּכֵּל בַּתּוֹרָה וְיִקְרָא בְלַחַשׁ עִם הַקּוֹרֵא. לִהְיוֹת מִן הָעֲשָׂרָה הָרִאשׁוֹנִים בְּבֵית הַכְּנֶסֶת. לַעֲמֹד בַּחֲצוֹת לַיְלָה לַעֲשׂוֹת תִּקּוּן חֲצוֹת בְּבֶכִי. וְאִם אִי אֶפְשָׁר לוֹ לָקוּם בַּחֲצוֹת הַלַּיְלָה, יַעֲשֶׂה אַחַר כָּךְ תִּקּוּן חֲצוֹת. לֶאֱהֹב שָלוֹם וְלִרְדֹּף שָׁלוֹם (עַיֵן לְקַמָּן בס' קצ"ח ס"ז). Means of amendment for a person who has succumbed to this sin, are recorded in the book, Yesod Yosef, which the author culled and gathered from holy and ancient books. Here I will cite some of them briefly: He should try to be sandeik, that is, to have babies circumcised on his knees (lap), and in particular to be a sandeik for poor families. He should increase his charity to the poor, observe Shabbos properly and honor it delightfully, and light many Shabbos candles. He should honor and love those who learn Torah. He should pray with fervor and tears. He should adopt the character of humility, and if he hears people insult him, he should be quiet and forgiving. When performing a mitzvah, he should do it energetically and with quickness until it warms him, particularly when preparing the matzos for Pesach. He should raise his children to study Torah, and train them to be God-fearing. He should raise an orphan in his home, and should treat him as he treats his own son. He should engage in the mitzvah of dowering poor brides. He should be called up to the reading of the Torah at least once a month, and recite the berachos aloud. He should look in the Torah, and read quietly along with the reader. He should try to be among the first ten to come to the Synagogue. He should arise in the middle of the night to recite tikun chatzos⁸See Kitzur Shulchan Aruch 1:5. with tears. And if it is impossible for him to get up in the middle of the night, he should recite tikun chatzos later in the night. He should love peace and should pursue peace.⁹See also Kitzur Shulchan Aruch 198:7.