"I will have a party on Friday."
It's a rabbit hole - I'm not sure it's worth going down it. They are normally the same thing in English but people love to make these topic/subject distinctions of ga and wa even though they often are hard-pressed to define what a topic is, in applicable terms.
This might help: https://en.wikipedia.org/wiki/Topic_and_comment
Some have suggested you use the "As for...A.., B...." model to see if it is the subject (eg As for work I like it. so Shigoto ga suki desu).
Since the topic/subject distinction is practically inexplicable you may wish to abandon it and use your own system for distinguishing the wa and ga - it will be just as if not more useful
[By the way, just in case there are those who emphatically think it is established in language teaching or linguistics, they may want to read this paper http://celta.paris-sorbonne.fr/anasem/asmic-papers/JapToGeneral.pdf which states "ga particle can refer to many other syntactic constituents than the subject itself (namely such as a location, cause, etc ) and a 'wa' particle cannot be systematically explained as a topic only"]
It is (as I understand it) also used when you/other actively affecting the state of an (possibly abstract) object.. Like: りんごをください (hope there's no mistake here). Here you're asking for an action to performed on the apple(s). In the case of パーティーをします (hope no mistake here also), the party is the (abstract) object, that you have/throw/create.
That is how this works as far as I understand it. That into account that 235日は日本語が勉強します (pretty sure I got that one wrong ^^)
I think the を needs to connect the noun to the verb, otherwise it would be a Yoda-speech equivalent in Japanese. Like "A party in friday I will have".
Not sure if starting with the day is the rule, I think the rule might be to start with setting up the context of what your saying, like (where, when, how) followed by the core of the sentence, like (have a party).
Take this with a full pack of salt since I'm new to Japanese myself, just a feel I've been getting.
Hey, this is a question for Android users : when swiftkey doesn't suggest it, I'm struggling with my keyboard to get パーティー written. I mean it can be hard to get the ティpart. Is there a tip for writting composed kanas ? I think it is strange that I have to rely on suggestions and not the typing itself. Do you guys use other keyboards ? Thanks !
は does not make any sentences habitual or future. は marks a topic and that's all. 金曜日はパーティーをします can mean "Talking about Friday, I will have a party." or "Talking about Fridays, I have a party."
If you need to clarify your intention, you add descriptive words to the thing that you wish to clarify. 今週の金曜日はパーティーをします - I will party this Friday. 毎週の金曜日はパーティーをします - I party every Friday.