One of the great things about training is the incredible sense of personal well-being you feel. It's a very personal experience, even when you're sharing it with others in the gym or even a training partner or coach. There are very few things that feel as physically and mentally satisfying as knowing you've worked hard in the gym and are getting stronger or going further than the week before.
Occasionally though, you're going to come across setbacks. If you miss a personal record in the gym, it can feel like a bigger problem than it actually is. The best advice I can give you is to follow some basic tips, which I've detailed here, and get ready for the next time, when you're going to smash it!
The first thing I would say is to take some time off. That might seem a little counter-productive, but having a couple of days away from the gym will help in a number of ways. Firstly, it will give your muscles a chance to recover and rebuild themselves. Secondly, it also allows your central nervous system an opportunity to recharge itself. The body works together to achieve some amazing things, so these will collectively be a great way to get yourself ready. Give yourself a little time off and avoid heavy lifting for 2-3 days and you'll soon be back to your very best.
In fact, the central nervous system has a big part to play in your training overall. By adding some speed work into your regime, you can fire up the CNS to spur you on to bigger and better things. You can, for example, try using lighter weights for much faster movements to build up your speed.
A lot of the work you'll be doing on resistance is through sets and reps. They are the building blocks of many training routines. Most of us will be familiar with them, but they often are ignored when it comes to changing things up a little. If you're working in the 8-10 rep range, working in conjunction on 3-4 sets, try dropping them to around 5-6. As the reps go down, slightly increase the number of sets you're doing; move them up until you're doing around 5 or 6 sets. By doing less reps, but more sets, you will be improving your technique and volume of the important movements you need to hit your goals next time!