One of the Rabbeim in my yeshiva way back when, in a mussar shmuz, mentioned two strategies against the Yetzer Hara:
1) He said when faced with a Yetzer Hara that looks overwhelming that you are afraid to even start the battle, it helps to "chop the Yetzer Hara into bite-size pieces." Instead of saying I'll refrain from lusting for a month, etc., say "OK, no Lusting from now until lunch. No commitment for after that, just for the next 3 hours. I can handle that." Lunchtime comes, and we say, "hey, that wasn't so hard, let me make a commitment from now until dinner. No promises after that. We'll wait and see." And dinnertime, rinse and repeat, etc. After a few days like this, then take on 6-hr. intervals, building up to a day, etc.
And if the Yetzer Hara tricks you, and I'll bet it could only happen "suddenly", don't beat yourself up over it. You didn't ask for this Yetzer Hara, and the fact that we've got it isn't our fault, so don't get depressed and ridden with guilt. Look instead at how much you've accomplished, how fantastic it has been all those days, hours, minutes and seconds of tremendous zechusim you built up when your were able to keep "sober!" Do we even realize the love Hashem has for us, how aware he is of our struggle to break free? Winning is not up to us, that's up to Hashem - all that's in our power to do is to keep fighting.
2) And the second strategy he said was, "If the Yetzer Hara trips you up, consider it like a punch. Are you gonna stand there and just take the punch? NO! So, PUNCH HIM BACK!! C'mon, give him a "PUNCH FOR A PUNCH." He messed up your count, so PUNCH HIM BACK with an extra blatt of learning that day, or some extra tehillim, or a little more tzedakkah, or make your next tefillah slower with more kavanah, or do a "random act of kindness," or call your parents just to say hello and tell them you love them, or someone who'd appreciate it or who is lonely, or spend 15 minutes quality time with your kids, get down on the floor and read or play a game with them, etc. And when you do it, do it with kavannah and say to yourself that you're getting even, you're doing this to punch him back, so you'll be able to get closer to Hashem.
Imagine how good you'll feel after giving him that punch back. You'll remember how much of a "winner" you really are. So feel good about yourself. YOU'RE DOING GREAT!!!
(Just a reminder: These are all "being on guard" tactics - and as we are are learning in Duvid Chaim's 12-Step Program, they are just temporary band-aids, they're not the real solution that's deep below the smelly onion layers... but hey, we're only into week 5 with DC, so we didn't get there yet :-)