I know it's Elul, and that this is the time to do teshuva in preparation for Rosh Hashana. But I also know that to do proper teshuva that is accepted by G-d, a person has to 1. verbally express his transgressions, 2. feel regret for having done them, and 3. accept upon himself not to do them again.
It's this last condition of teshuva that I am having difficulty with. There are some things which I'm nearly certain that I'll lapse into again at some point. The proof is that I did "teshuva" on them last year, and here I'm confronted with them again this year. So to do teshuva on them this year seems hypocritical. How can I do teshuva on things which, no matter how bad I feel about them now, I know I'll probably do again at some point? On what basis can I claim that I'll not do them again? So what's the point of doing teshuva on them?
I fully understand your perplexity. Since a condition for teshuva to be accepted is one's commitment not to do it again, if he "knows" he'll do it, there seems to be no point in doing teshuva, and what's more, doing so would seem to be hypocritical.
Although this is a very good point, there is a slight inaccuracy in your perception which makes a world of difference.
The condition is not that you never do it again, but that you accept upon yourself not to do it again. The difference is that a person has to make a firm resolve not to transgress this prohibition again, and to proactively design strategies to prevent himself from even being challenged by the option.
If he sincerely does this, he has done teshuva, which is accepted by G-d.
Now, as time passes, if a person is caught by surprise, lets down his guard, or even slip-slides back into that transgression, that doesn't undermine the initial teshuva that was accepted. True, he'll have to do teshuva for whatever responsibly he has in having transgressed again, but this is a new reckoning which is independent of his prior teshuva.
So even if a person relapses onto what he firmly resolved not to do any more, if he truly accepted in his heart of hearts (and G-d knows our hearts) that he regrets having done this and truly doesn't want to do it ever again, that's teshuva.
Since this is true after the fact, it is also true before the fact. A person must not be discouraged from doing teshuva because he anticipates falling again. The main thing is to work very hard on expressing and internalizing the regret for having done it, and the sincere desire and intention, together with a practical plan, not to do it again.
Another point to consider is that with this approach, even if one does lapse into his "old ways", he probably won't actually go back to doing the same thing again. By which I mean that, more likely than not, he won't transgress with the same frequency and intensity as before. This is because his teshuva will probably limit how often he does it, and his guilt will limit his enjoyment of it. This is also teshuva, even if only partial, which, if he's persistent and consistent, will eventually enable him to overcome the challenge.