Dialogue tags are basically modifiers of - you guessed it - dialogue. With such tags, you need to be careful about capitalization and punctuation. 

Here are a few examples:

1.) Notice I'm using a small first letter here for the dialogue tag. You can never use a period to end your character's dialogue with this type of tag.
"Hi," she said shyly.
"What are you saying?" he asked.
"Oh no," the girl exclaimed.

2.) Period, capitalized-first-letter format. Conversely, you can never use a comma to end your character's dialogue for this type of tag.
"What?" He looked at me angrily.
"Thank you." Her voice was cold when she said the words.
"Hmph." That was all he said - hmph.

ADVERBS IN DIALOGUE TAGS
Now, if you've started reading books on how to write fiction / novels, then you'd probably have noticed that editors are very much discouraging when it comes to the use of adverbs.

"I hate you," she said furiously.
In this case, there's no need for the adverb since you can infer the character's not feeling predisposed to whoever it is she's speaking to with her dialogue alone.

"I hate you," he said quietly.
Ah, but in this case I think an adverb is warranted. Because you gotta wonder - why did he say such powerful words quietly? 

WHEN AND WHEN NOT TO USE DIALOGUE TAGS
It's a subjective matter, but it's safe to say that you don't need to use it all the time. 

P.S. Please do not consider this post as an indication that I'm a great writer. I am not. 

So...I've always wanted to share some stuff about writing but I've always thought I didn't have the right to. After all, it's not like I'm one of the greatest writers out there. Right? I know that. BUT I realize that because of how much writing I've been doing the past years, there are things that I do know more than those who are just starting out.

Which is why I've decided to start my Quick Tips Series and they are geared for aspiring authors who wish to polish their work. 

So first tip - the use of tenses. Always remember that you need to use the SAME tense throughout your book.

THE RIGHT WAY
"Hi," the girl SAID. 
The boy IGNORED her. 
She REPEATED, "Hi."
The boy still DID NOT look at her.

Above, we've used PAST tense throughout the scene. 

THE WRONG WAY
"Hi," the girl says.
The boy ignored her.
She repeats, "Hi."
The boy still doesn't look at her.

Now, with the above example, I've mixed past and present tenses. That is a huge NO-NO. Like, one look at your sample pages and agents you're querying will immediately hit 'delete'. 


Now, if you're thinking - which tense should I use? 

Good point!

I think it's safe to say that PAST tense is the conventional choice. However, it's become increasingly common for present tense to be used in YA/NA/Erotic romances simply because it makes the story feel more intimate, like you're really a part of what's happening. 

Ultimately, this is a subjective choice, one that has to do more with your writing style and preference.

Just be aware that there are a number of agents and publishers who distinctly dislike the use of present tense. We can't blame them - to each his/her own. :) 

P.S. Please do not consider this post as an indication that I'm a great writer. I am not.