The first step is to be honest with yourself about the extent of your challenge.
You've "stumbled here and there." Is it getting worse? Have you tried to stop but can't? Are you also hooked on mast*? Inappropriate thoughts, fantasies?
Practical advice for "how to control one's self when certain things walk around in the streets (especially in the summer time)?" --
Feed it and it's hungry. Starve it and it's satisfied. The way to control your eyes in the summertime is to control them in the wintertime. Don't look at women. Period. Not their faces, their hair, their arms, their nails, or their sneakers. Not ugly ones and not pretty ones. Not live, not in the newspaper, not on the internet. Tznius or otherwise. Pinch yourself hard when you catch yourself looking.
The best way to stay away from shmutz on the internet is to stay off the internet altogether. The Y"H isn't going to tell you "Torahyid, go look at p**n." He's going to tell you to look at some benign site. Once you're comfortable and alone at the computer, he'll slide you right to where he wants you. So if you must get on, commit to using only a computer where someone else can see what you're doing. Otherwise know you're in trouble from the moment you sit down. Be honest with yourself. If you can't fight it, then you're only hope is to avoid it entirely.
But if it's more than here and there, if it's a growing pattern, then you may be addicted. For that you'll need a recovery plan, which requires a bit more work. It's well worth it though. Living in active addiction isn't living. But you can reclaim your life, your mind, your sanity. That's where I am.
Welcome!
Alex