One of the biggest aspects of a powerlifting meet that gets overlooked especially by beginners is how to manage your day at the meet. You can be the strongest person in the world and have the most incredible training cycle of your life leading up to a competition, but if you don't have at least decent meet management skills you won't be able to transfer much of it if any of it to the platform. Unfortunately, lots of us have had to learn these lessons the hard way by forgetting things or bad timing on warm-ups etc etc. Here are some basic things that should help you avoid some of those mistakes!
Have a meet day Check List.
This checklist needs to consist of all of the things you will need to bring with you to the meet and/or things you need to do at the meet. If you are an unequipped lifter that list will be relatively short as you will need a kind of specific shoes that you need for squat bench or deadlifts, your singlet, your belt and other basic necessities. Things like your own chalk, tape and baby powder are universal items you can use at a meet regardless of division of course. When we get into more equipped lifting that list gets quite a bit longer with squat suits, bench shirts, knee wraps, wrist wraps and other tools that you use to help set those pieces of equipment up like a wrap roller or belt tensioner. If you have medications that you take like anti-inflammatories or use muscle rub ointments you can't forget to take those either as that kind of mistake can ruin your day completely. The best way to make this list is to go over any meet day specific things that you need to bring ahead of time and then consider every single thing you use when you train your primary lifts. It's very easy to overlook some of the smaller things you use in everyday training sessions. Paying attention to those details will help make sure that you have as good of a meet as possible.
Selecting your attempts.
There are lots of different schools of thought on how to pick your numbers within the confines of three attempts on the platform. I spent years and years contemplating on how exactly all three of my attempts would go for each lift at a meet. In reality you generally don't know anything about what you are going to do until you get your opener in the meet. I generally recommend setting your opener at 90% of your best clean single and training. This does require you to be completely honest with yourself and if you have a bad lift and training that you think is your max that will throw this off quite a bit. That's another instance where you need good honest training partners and even better than that, video footage of yourself doing the lifts. Others will say you can open with your best double or even a triple if your wanting to be pretty conservative and make sure you are going to get in the meet. In my very first meet I had it explained that it didn't necessarily matter that I opened extra light because there was no limit to how much I could jump up to if I wanted. I probably should have been limited on some of the stupid jumps that I've made over the years here and there but you would be surprised how many meets are won against superior lifters just by getting in your openers. On second attempts anywhere between 95 and 100% of your best rep in training is a good guideline to follow. You just have to play that part by ear after getting in your opener first. Third attempts can be used to conservatively build totals or shoot for the moon for PR's and records. Just be sure to know what your priorities are here in the reason that you came to the meet in the first place.
If there was ever a single thing I would say to be the most stressful and panic causing aspect of lifting and a meet it would be knowing how the time your warm-ups before going to the platform. The general rule I follow for squats is to allow one minute per "raw" or minimally equipped lifter, a minute and a half for a lifter using knee wraps and anywhere between a minute and a half to two minutes for a fully equipped lifter. This way if you look over the flights (group of lifters doing their attempts together) posted at the meet to see how many people you have before you you can count the lifters ahead of you in your flight and even the flight before you. The way I recommend to do this is to count backwards from your attempt in the flight for however much time that you need between your last warm-up until your opener then backward from your last warm-up to your second to last warm-up etc. For example, let's say all the flights have 15 people in them and you want 10 minutes between your last warm-up and your first attempt on the platform. If for instance you are number 10 in your flight of unequipped lifters then you would count backwards 10 people (for 10 minutes, 1min per unequipped lifter) or so to take your last warm-up. That would mean you take your last warm-up when your flight is just about to start. If you are at the beginning of your flight then you would take your last warm-up when the fifth person (out of 15) in the previous flight was lifting their 3rd attempt. You would follow the same pattern counting backwards and attempts to make sure you are on schedule with enough time to get and all of your warm-ups before having to go to the platform. For bench press and deadlifts I would just stick to one minute per lifter when timing your warm-ups. Deadlifts generally fly by quickly and there isn't a ton of difference in time taken between equipped and unequipped bench pressers.
Food Through The Day.
Not having food to eat through the day can really catch up to you on your later lifts. It's usually very hard for me to eat anything on meet days but it's just something you need to do if you are trying to perform at your best. My go to meal between events or lifts is a peanut butter, banana and honey sandwich on whole wheat bread. There is some protein but primarily lots of carbs and a moderate amount of fat that all supply energy and a nice even release of carbohydrates. You really don't want to live on refined sugars or other short acting carbs as they can cause an insulin spike leaving you lethargic for a couple of hours. It may take some time but figure out what you can eat easily and carry.
The absolute best aspect of strength sports in general is getting to go to competitions and meet other people who have the same passions and interests as you do. If they didn't they wouldn't be there right? I have met many of the people that I value the most in these kinds of competitions and have been able to call them friends for well over a decade now so I would encourage you to always be friendly, help out strangers even if you may be competing against them and introduce yourself to people there. There is simply too much to gain and very little risk to not put yourself out there little bit. There have been countless times that people I offered to help out six, seven, eight or more years ago at small meets have come up to me and reintroduced themselves talking about how much they appreciated the help forever ago or any positive karma that comes back like that. Some of those people have really helped me out of a tight pinch at a meet when I was desperate for help and without paying it forward to begin with I could've been in a real bad way competition wise. Just be sure to pay those good deeds forward because it can come back to you tenfold when you need it the most!