Tips for becoming a taser / making pit hacks

I would personally recommend sticking with Snes9x or using Bizhawk for learning to TAS. Both are more user-friendly than lsnes, with Bizhawk having a few more useful tools (but also being less user-friendly and more performance-intensive than Snes9x).

Anyway, the first thing you should do is get acquainted with the tools you're given; knowing what you can do will make things a lot easier.
Frame advance is, of course, the most basic, and one you should get comfortable with using.
Lua scripts can also be useful, particularly this one, which can display a lot of information you can't normally see in-game. As an alternative, you can also use a RAM watch (another tool).
Macros (Snes9x only) are another useful tool that allow you to repeat a sequence of button presses automatically (for doing 6/5 or 1/1, for instance). Unfortunately, Bizhawk/lsnes don't support this without writing a lua script, though.
TAStudio (Bizhawk only) is also an interesting tool that lets you record and edit an input movie at the same time, and serves as an alternative to the savestate-loadstate style TASing normally involves. I recommend trying it at least once to see if you're more comfortable with it; it's easier to show than explain.

Second thing you should probably do, of course, is get to know SMW itself. Knowing what you can do is pretty important in designing difficult levels and figuring out strategies for other people's levels. I'd recommend skimming through TASVideo's game resources page for a brief introduction to tricks if you haven't already, and trying an easier pit hack or two to get the feel for it (don't need to be too serious about it, just focus on getting through the hack first before trying to optimize anything). If you use Discord, you could also join the SMW speedrunning Discord for help since a lot of TASers tend to be there.

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Professional frame-by-frame time wizard. YouTube - Bluesky - SMW Glitch List - SMW Randomizer

lsnes also has a TAStudio-like tool, but it's much harder to use and I personally don't recommend it.

Bizhawk is much easier to use than lsnes in my experience, but feature-wise they're about even (TAStudio aside). lsnes has one notable advantage, though, in that every savestate is actually an entire input movie, so lsnes is actually always recording; this can be useful if you accidentally forget to start recording when working on a TAS, or you come across something by accident and you want to check how you did it.
(snes9x I personally just prefer for casual work, since it has the most intuitive design, but that may just because it's the one I've used most)


As for hack recommendations, if you're looking for pit-difficulty, trying Pit of Despair/Death or the original Item Abuse would be good starting places.

If you're not comfortable with them yet, you might want to start with more standard Kaizo hacks, such as the original Kaizo series, Super Dram World, or Super Panga World, or harder hacks like Cool or Cruel / Mario Must Die (I'd recommend checking the Kaizo: Light/Hard filters in SMWC's hacks section for more).

Lastly, if you'd prefer to just start with the original SMW, I'd recommend trying freeruns (go into a level and see how much you can do with it). This is a good way to get acquainted with the quirks and glitches in SMW, and I'd recommend searching this glitch list for things you can do with the sprites and items in the level. There's no real bad levels for this in SMW, to be honest, since it just comes down to how much you can find to be usable. (there's a good number of them on YouTube if you want to see a few examples)

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Professional frame-by-frame time wizard. YouTube - Bluesky - SMW Glitch List - SMW Randomizer