Comma

Comma splice

You can not use comma to directly connect two sentences.

I really appreciate your willingness to help, I’m excited to get more feedback from you.

Here comma need to be something stronger: ., or maybe ;

However

Same as the above, you can not use a , before however. Between two independent clauses.

Before However, it is always right to use ;, but some people do not like . before However. Some boss does not like you to start a sentence with However.

Conjunctions

Adverbial Conjunctions

However is adverbial conjunction.

Moreover, Instead, Otherwise, Therefore

You can start a sentence with Moreover, Instead et al

• when an adverbial conjunction connects two independent clauses in one sentence, it is preceded by a semicolon and followed by a comma.
• if an adverbial conjunction is used in any other position in a sentence, it is set of by commas.

Coordinating Conjunctions

FANBOYS: for, and, nor, but, or, yet, so

• when you have two independent clauses connected by a coordinating conjunction, it is generally a good idea to include a comma.