Well, try to include some kind of strategy. I use my sun team, for example, and while sun isn't the best weather condition, I use it to boost the power of the pokemon in my team (which are good even without weather). My sun team has these basic kinds of pokemon on it:
Weather creator (if a non-weather team this can be any beneficial role really) (ninetails)
Tech (annoyer) (breloom)
Keep in mind you need to have a good, balanced typing in your team too. All pokemon on my sun team are fire or grass, and this comes in handy when going up against any other weather team, or normal team due to the balance. Also make sure you have a balanced moveset with moves that cover a wide range of types. Keep your sweepers and stallers balanced; leafeon is a physical attacker and volcarona is a special attacker, while heatran stalls both physical and special. Surprise your opponent with something they won't expect; I personally like putting an ice-type move onto one of my pokemon to surprise the opponent when they send out a dragon type.
All in all, be creative, experiment, and you'll have made an invincible team in no time.
Leafeon isn't actually good in competitive battling, the best Grass Pokemon in he tier is Breloom, and after one Swords Dance, Technician boosted Mach Punch is actually hard to survive.
If you don't want to use entry hazards/weather, I suggest to use a Volt-Turn tea m - in which 4-5 of your Pokemon know the move Volt Switch or U-Turn. I can battle with you some time to show you how good and fun it is.
If I go offline during a trade or a battle, please forgive me as my country is in a crises regarding electricity.