How do I learn to keep my bike going straight when I ride (new rider)?

I didn't ride bike for more than 20 years, not I just got one again, 21 speed cruiser style, I notice today when out riding in my neighborhood that I have a hard time keeping the bike going straight, will this improve as I "re-learn" or am I doing something wrong?
I am overweight and out of shape, but hope riding bike will help.

It'll get better with experience, as long as you work on it. Practice a smooth pedal stroke, keep your cadence up so you're not lugging the engine, and try to keep your upper body relaxed.

yes it and you will improve.the faster you go the straighter it will ride.the slower you ride the more you have to physically balance the bike yourself.and yes riding will help.try keeping your gears at 2 in the front and 3or4 in the back, when that is to easy move the back gear up.

Do not expose it to those gay lifestyles,keep it away from frisco and don't let it listen to that public radio and it might keep straight.

try using a line to guide you, if you are riding along the road, try to stay near or in the line. If your not on the road, try using an imaginary line. It takes time, but that's how i learned.

Go faster and get better tires if yours are bad ones. They make tires for all kinds of different surfaces. If you are overweight get a wider tire with a smoother surface. They are more comfortable.