This is my red/white swarm deck.What can I do to make it better? http://deckbox.org/sets/468864

Is this for casual play? Or competitive like FNM? What format are you aiming for? Standard? Modern? Others? What sort of budget are you looking to spend to improve it or do you only want to work with cards in your inventory?

Please, you need to provide more information so that we can provide the best input possible.

This is for FNM, maybe a Grand Prix I'm not sure on that yet but a standard/modern deck

First off, you need to pick between standard or modern as both of them have considerably different decklists that perform well.

Secondly, the deck is full of far too many 1-offs that don't see much competitive play. You need to build something that has 3-4 of most cards to ensure it has consistency. To name just a few of the pieces you really just don't need/want to run in here: Goblin Arsonist, Warclamp Mastiff, Goblin Shortcutter, Hellraiser Goblin, Staff of the Flame Magus, etc etc

The real question is how competitive you really want to be. You can easily brew your own list using seldom used stuff, but be ready to lose a lot of games at FNM (or all your games at a GP). However, if you're wanting to compete, my suggestion, as much as it pains me to say it (as I despise net-decking), would be to look on TCGPlayer's decks page for the decklists that are finishing well that are closest to what you want to do. Then make small adaptations from there.