Look guys/gals, only about 2% of regulus players are good with him. And there is a regulus in every game, nearly every team, on PUG games. Let's just make an assumption and say that you aren't one of the elite.
Here are some pointers. I know you're probably new to the game, and the real machinations of fights are a little foreign.
-Standing back and sniping does not help your team.
Why? Because one of your teammates is trying to hold a lane in a 2 versus 1. You need to find someway of getting in there and making it a 2v2. Remember, if you keep moving ("twitching around"), you will not auto-attack. You need to keep auto-attacking. Get the idea?
-Getting kills does not mean you are doing well.
Why? See pointer #1. You aren't "earning" those kills. You're stealing them or just getting the last hit in as they run. Spending it on yourself will cost the game. You need to spend 90% of that money on your team's upgrades. If you are a ways from an upgrade, buy an item for yourself, but be ready to sell it THE MINUTE YOU HIT THE WAR SCORE LEVEL that you need for that team upgrade. A regulus with 5000hp still gets pwned by a UB or pretty much anything.
-You better have mines. And you better NOT throw them on creep waves if it'll drain your mana or if a DG fight is brewing.
Why? That's your biggest contribution to a lane fight. Run up and throw 1200 dmg worth of mines on the enemy, plus slowing him. That turns fights. That wins games. Practice your throw, aim for the guys feet. Don't throw behind him or in front. "In case he runs" does not help your dying teammate. This is not about you, it's about the guy you are supporting (and you are support). Ask anyone, you can't count how often a reg player will waste all his mana on creeps and then float off during a fight with "oom".
Those three pointers will help out more than anything else. I would suggest getting maximum speed and a few hp items. Most builds call for "no scope", but I disagree. Maybe a pro player doesn't need that, but we're not pro's, now are we? You need that max range, to stand behind the DG your supporting, auto-attacking his target and throwing mines on the enemy. When they come after you, you run like hell. If you're super fast, you'll get away quick and can turn around and re-engage. Max mines will slow the enemy, also, which is a huge boost.
It's not about kills, it's about holding a lane. You probably can't do that, especially with a DG right there. You need to link up with a teammate, and work to support him/her. I can't count how many games that we've had a useless reg (pretty much all games with reg). And he thinks he's superman since he stole 9 kills, then buys gold and priests and never again helps out.
Look at the big picture. If your team is constantly falling back from lanes, your losing. If your team is not dying very much, but you're still losing, it is PROBABLY because of you. Because regulus is weak and it's 3 versus 2 out there, with you contributing a measely 20% of what any other DG would.
My biggest advice would be to stop playing regulus to hide from the fight. Pick a tank DG and practice some, learn how it goes. Sedna is way more useful in a fight as a support DG, but if you MUST play Regulus, play him stronger. Saving your own skin and buying items for youself is costing the game, AND IT IS YOUR FAULT.