Its pretty good since you've just started writing, I remember when I first tried to publish something back on FF.net, it was a quarter of the length of this and pretty boring
The dialogue is pretty solid, and I was able to get a gist of the personality of the characters pretty easily.
However, there are a lot of things you could do to strengthen your writing and the story. First off, while the dialogue flows nicely, there is a lack of overall expression and emphasis on how the characters are feeling, and their emotions. Don't be afraid to write in adjectives and explain what the characters are experiencing as they talk. Like when Rainbow Shine gets extremely excited when she finds out she's going to Las Pegasus for the first time for example. Show her excitement, show how overjoyed and surprised she is. This kind of stuff adds meat to the bones of the story
Also, try using some description on some things. Show us how the weather is, or what a place looks like. For example, the inside of the bar they ate at, what did it look like? What kind of people were eating there, was is darker, was it an older bar or newer, do the floorboard squeak, is there even floorboards? etc etc. It adds a nice touch to be able to fully create an image of what your reading, and this goes for characters as well.
I'll give you an example of what I mean.
_____
The group made their way into their favorite bar, and were greeted with a bountiful amount of smells and sounds. A very enthusiastic bunch of colts were living it up by one of the corner televisions as they cheered their favorite hockey team, while their waiter chuckled in amusement as she watched. One of these waiters, a blond colored colt with red hair, passed by with a piping hot plate of chips and queso, causing Sport's mouth to quiver with excitement at the potential taste he would receive soon. They made their way to the front desk, anxious to get some grub in their bellies.
"Hello, welcome to the Cider Barrel. How can I help you?" The waiter questioned nicely, sending a smile their way. The sporty pony seemed as chipper as can be as a waiter, donning an orange Cider Barrel t-shirt along with Ponyville Cardinals cap, her long mane flowing out the back of it in a fashionable ponytail.
___
This is the kind of stuff I meant. I'm not trying to bash the story at all in the slighest, and if I'm coming off as harsh at all, please let me know. I'm just trying to help out a bit buy giving you what I've learned from writing.
I'm looking forward to chapter 2 btw