Which app do you recommend?
Here's a simple guideline for you. Tinder is a good open ended one now. It was really in its prime as a hook-up app up until maybe 2015. That's what it was used for and everyone knew it. Now people are on there for other things. But one of the cool things about it is that it can lead to anything. If she swiped you and your pic actually looks like you, it's mostly safe to assume she's thought about hooking up with you and would under the right circumstances. A downside (or upside) is that it's more shallow, and a lot of it is based on looks, but the good thing about that is it gets that part out of the way.
Bumble is okay. it's kind of like Tinder, but if you match with someone, they have to speak to you first before you can message them, I like taking the lead, so it sucks to have to wait for someone to message you. As with everyone, we are all busy and I think they only have like 24-48 hours to message you before you both unmatch, so if a girl is busy then she may not get to you. If you get bumble I advise not even swiping anyone during the weekend.
Bumble is basically Tinder for girls that are tired of getting so many unsolicited dick pics lol.
OKCupid or even Match are better if you're looking for an actual relationship. Especially Match. It has a reputation of being lamer, but there are some quality girls on there.
Having a good profile pic is key. I assume you're a guy. No selfies. A fairly current well lit pic that shows you from the waist up is good. If you don't have a pic of yourself that isn't a selfie, have a friend take one for you. Follow it by a pic of you with a dog if you own one, a pic of you with some friends (preferably mixed company), or you doing an activity that you like. All of these aren't required, but they help. A clever bio is god. Short and sweet. As far as messaging girls, I stay away from anything like what's up, or how's it going, etc. Those are boring. Most of these girls are receiving a ton of messages, but the good news is that most guys are sending boring shit. So make yourself stand out. Ask yourself if you'd reply to your opener if you received it. If you wouldn't, send something else.
I also stay away from compliments, unless it's followed with something cheeky or a question. Don't put them on a pedestal. Their inbox is already flooded with guys telling them how gorgeous they are. You matched with her, so she already knows you find her attractive. Compliments don't usually get much a reply beyond "thanks!"
I try to make a comment about something in one of her pics or something in her bio, or make a self-amusing statement, or ask her a question that isn't yes or no. Everything is geared towards setting up an actual date to meet, and getting her number to message her off of the app. Even using proper punctuation and grammar goes a long ways. Self amusement is important. Just treat it like a video game or something. It's supposed to be fun, and not stressful or a chore. Send shit that you think is funny, direct your messages towards meeting, try to get her number to message her off the app, and try to set up a date within 48-72 hours, tops.
I have more that I can PM if you're interested. This is getting to be lengthy and I don't want to annoy people or hijack the thread.