I've learned a few things over the past several months of playing STGs:
1. When enemies are shooting directed shots or scattered directed shots and trying to corner you, it's advantageous to shoot while moving diagonally towards them. They will have to play catch-up and rotate more, creating larger gaps in the enemy fire. Next, back it up to the bottom of the screen and do it again the other way if there are still more coming.
2. Strategic alternation between focused shot and standard shot can be extremely helpful in controlling speed. Sometimes macrododging is the quickest and safest way to survival when bullets are less dense, but fast. In this case, use the standard shot to gain speed, allowing you to avoid an entire pattern instead of trying to filter through it. But let's face it, sometimes you have to tap your way out of some thick, slowmotion bullet syrup. For crazy density, micrododging is key. Focus shot can often slow you down for increased control.
3. Some games have bullet canceling enemies. These enemies are actually your friends. It's probably best to try and remember the locations from which all enemies emerge, but it's especially good to remember these dudes. In a tight squeeze, you really want to be able to focus on what is directly in front of you (or a few ship lengths in front of you if it's coming in hot). Knowing where these bullet canceling enemies are without having to look up the screen is crucial because they can grant you relief through all that dodging once you destroy them.
4. Almost every cave game has a part in which swarms and swarms and swarms of enemies come flying at you, very fast, while firing directed shots. Normally you'd think, "there is no way in hell (no pun intended, no really) I can dodge that." But you can! Before the swarm, start as far left or right (depending on what comes after the swarm) as you can and slowly tap toward the other direction. As those fuckers fly down at you, just tap tap tap along while strafing horizontally. The idea is to stay one hairlength in front of the enemy fire while taking these dudes down. Hopefully you can destroy all of the enemies before you reach the other side of the screen. If you run out of room, you might be totally cornered. If this tactic doesn't work, try tactic 1 next time.
5. Point-blanking is the shit. There are a lot of benefits to point-blanking. One, being scoring. Most of these games award you for being brave and aggressive. Refer to individual strategy posts about scoring techniques involving point-blanking. Also, from a survival standpoint, point-blanking is often useful when you have stages where masses of patten-type enemies swarm the screen. The idea is to kill as many as possible as quickly as possible before they flood the screen. Because honestly, once you have pattern on pattern on pattern, it gets really hard to dodge all of them, unless, of course, you know exactly where and when that next bullet-canceling friend will come along.
6. Don't always straddle the bottom of the screen. It's kind of like snowboarding. When you first go hit the mountain, you notice that the speed starts to get intense and want to lean back because you're afraid. But, as anyone who snowboards knows, leaning back just means you will loose your ability to control your snowboard as you turn. Translation: you will catch an edge and eat shit, because you will lose range of motion and control. That's kind of what happens in these STGs. You play a shooter for the first time and see all of these scary bullets, moving to the bottom of the screen in fear. Again, this will lead to you eating shit, as you will not have full range of motion. Being able to move in all directions puts you at a really big advantage while dodging. Certainly, there are exceptions, like when riding pow or dodging the fastest patterns of all time (or what seems like it).
7. For people who savestate: grinding through one part of a game over and over again sucks. Sometimes, it's a lot better to just play through the game and come back to it again fresh. Trust me. It's kind of like skateboarding. Say you're skating with your friends and having a good time. You get to a spot and you try to hardflip this 5 set. Oh no, it's 10 tries and you still haven't landed it. Now 15. Now 20. Now you're pissed off and bruised and want to keep trying it until you land it. Well, at this point you're letting your ego get the best of you. Chances are, if you keep skating and try some other tricks and come back to it, you'll land it first try. This is kind of like STGs. Savestate grinding can really burn you out, in addition to choke the joy out of playing games. If you find yourself in hockey temper mode during savestate practice, just play some full runs. You won't get so hung up on that one part and have more fun. Suddenly, what do you know, you just dodged that totally dense pattern and destroyed TLB. Another good idea is to...put...the...controller (or stick)...down.
8. If you die somewhat early on in the game, don't automatically restart. I know, your impulses want to restart. You think, "I want to have the best starting advantage to produce the best score, chance at survival, etc." But, sometimes you can make an early mistake and totally kill it (at least by your standards) later on. This happened to me recently, so I'm sorta sticking with it.
9. Listen to that guy Sapz, cause, I dunno, he's really good and shmup wise.
10. Don't copy that guy Sapz. His techniques are likely too advanced for you, and you will eat way more shit. In fact, you really shouldn't copy anyone all too strictly, especially starting out. You'll lose the ability to actually improvise, which takes some skill. Sure, it's good to follow loose lines to get ideas, but pixel copying won't improve your skill as a beginner.
That's all I got. I pretty much still suck, but I've noticed some improvements in my gameplay and overall joy in playing shooters. Perhaps advice in this context will be helpful for other beginners as well. Goodnight, and good luck.