Does anyone have any tips for first-time fanfic writers?

My best advice would be - have fun! Focus on what's most interesting to you. Write self-indulgent stuff! 

Being canon-compliant is secondary to having fun while writing. People can feel when the author genuinely enjoys the writing process. 

If you're stressed out about characters being OOC, I'd recommend doing a little exercise: write down the most prominent character traits, values and small but characteristic quirks of a character. It usually helps me. I do it even with my original characters for my book when I feel that they sound OOC - it helps with focusing on the most essential stuff. :3 When you do that, you can "filter" their behaviours through those traits. For example, if a character is loyal, brave and secretly scared of rejection, they probably wouldn't ditch their friends in a dangerous situation. And if they did, the circumstances would need to motivate them to do it by playing on those core values. 

Writing dialogue is hard as fuck - I just act it out either in my head or out loud. It often still sounds a little stiff, but it improves with practice. 

Just write what you like, and write as often as possible without overwhelming yourself! Remember that fanfiction should be something you do for fun, and you don't have to be perfect. Everyone's first ff is a little awkward, so don't worry about it :]

> [snip] I want to know how other writers keep the canon character but still get to be creative for the sake of an interesting story.

I don't want to steal what @Hades said above me since those are some PERFECT points about how to get proper (or at least good) characterization across when writing fic, so here's my thoughts:

- I once read on another internet forum that giving your (or in this case the) character(s) questions about their motivations can help, so start with "asking why" about the character's motivations and go from there. (here's a good post from Reedsy about it)

- It's OK if you don't have the character's voice down right away as you're "asking" questions - that can be fixed later while writing your story and editing.

- You could also put the characters in absurd scenarios (eg, an Alternate Universe or What-if? setting) and try to figure out how they'd react. It can be pretty fun, and sometimes you get further insight into their characterizations that way.

Which leads me to your next question:

> I also have problems with writing dialouge so any help on that front would be intergal

I would suggest reading/watching plays for this - it makes it easier to "visualize" dialogue without having too much setting descriptions.

Of course, plays are not the only thing you can use, and to paraphrase a user on a writing discord server I'm on, you can read movie and show scripts (on sites like IMSDB), especially those you really enjoy, to get a sense of how the writers nailed the dialogue.

To paraphrase another user on said server, you could also "roleplay" a scene with friends or other people (eg, in a chat room or other text-based medium). Kind of like performing the role of a GM and player simutaneously in a TTRPG, I think?

I'm also gonna echo what @Hades said above me -- the most important thing to keep in mind while writing fanfic is to have fun! And practice makes perfect!