I am not a native, but I have studied Japanese for many years. My advice in studying the language is simply to use the language as much as possible. Don't be afraid to practice with natives and use the skills you have learned. For example, every time you learn a new grammar concept, write it down in a notebook, followed by 4 or 5 example sentences that you create and have those checked by an advanced speaker or native speaker. Language is learned best when it is put in action, because the application of the language helps you to associate concepts with words, so those words don't merely have sound, but meaning as well. Also, looking at your sentences: 「ごご　じゅうじ　に　ねます。」is correct. There are no errors here. 「らいしゅう　にちようび　きょうかい　が　いきます。」has one slight error. At the end, you should replace が with に or へ に is a grammatical particle that indicates a location. So, if you translate that into English, に is sort of like the preposition "to." に, also indicates time, so you could potentially say にちようびに, but it can sometimes be omitted in speech. へ also works, as it indicates a directions. So saying へ is like saying "in the direction of." が indicates a subject, so saying きょうかい　が　いきます sounds like you are saying that the building itself is moving. Does this make sense? So, the correct form of the sentence would be: らいしゅう　にちようび　きょうかい　に　いきます。 Keep in mind, that I only put spaces between the words to make it easier to read. Normally, Japanese is written together in one line, like this: らいしゅうにちようび、きょうかいにいきます。(with kanji: 来週日曜日、教会に行きます。） I hope this makes sense. Please let me know if there is anything that is unclear.