I keep getting my ass handed to me and it's infuriating. This is the first Nintendo game in a very long time I'm not at least pretty solid on so it's incredibly frustrating. For those that are fairly highly ranked or win quite often online, what are your tricks and suggestions?

Use fast characters. I can really tell the difference.
Other than that, be on the defensive more than the offensive.

I'm not the best ARMS player obviously, but I think it's a matter of knowing the characters and arms well. Knowing your enemy's weaknesses, and their arms weaknesses will give you a great advantage. Also, be defensive. Try to counter-attack you rival. That worked for me.

Grab as much as you can.

Understand and master movement options. Once you do that (and believe me, you have not yet), you can start to learn your opponents patterns and adjust your attacking and offensive approach accordingly. Being patient is very crucial but you must master the flow and pace of the game.

Even though you may like a character, you have to understand that you may not know yourself as well as you think you do. Find the character that you feel like you can grow with going forward as opposed to a character that you think you will do well with today. Learn to use every arm type but find three or four that you can start your mastery on today.

Lastly, watch a lot of videos: of yourself and of other, better players. Watch yourself lose and be very critical. Ask yourself what you were doing wrong and then make adjustments. I know this sounds like it will take a long time but if you follow these steps basically in order, you will see progress in a matter of days and you will start to reach your upside and raise your potential not long after.

Learn to read you opponent. Reads and predictions are important in all fighters but I'd honestly say they're the core of the combat in arms. Just pay attention to their movement and learn to exploit any patters and habits they have. Also grab spamming is for scrubs, it's punished really easily

Learn the perks to every character. Also if you hold the dodge button, block button, or land after jumping without attacking, you will activate the perk to your arms if you attack right after.

Personally, I like to jump and throw single punches with my arms activated. I only grab when my oppenent is off guard or blocks way to much. Also try to time your overload during one of your opponent's attacks, or they can dodge or block it.

You basically nail it in the head. Plus don't expect results right away or over night. Getting better at anything is always a process. There are no short cuts to success. Sounds corny, but that's why professionals are successful at what they do.

You honestly think someone who's brand new to the game has an equal chance against a person with 100 hours of experience? You can get better at ARMS the same as any other game.

-Lonely_Dolphin

You have to find the 1 Character and 1 Combination of Arms that really works well for you.

Always charge and jump

Dont hesitate to try a different tactic halfway into the match

If you are far away, still keep punching to get your Super power up.

But my first line is very important.