Goodbye to All That, by Robert Graves, paints a pretty graphic depiction of life and death in the trenches and goes into trench raids quite a bit. Graves trained to become an officer in the Royal Welch Fusiliers (a regular army battalion), but ended up being deployed with the Welsh Regiment (territorials). His reflections on trench storming vary quite a bit between the two units – everything depended on the circumstances. Who were you attacking, and how long had they been on the line? Were you attacking during the day or at night? Were your attackers particularly keen or experienced at going over? Graves wrote a lot about how the Welsh Regiment was primarily composed of miners, who, while being excellent diggers, were not too pumped about lobbing grenades into German trenches. They spent most evenings spraying the German lines with rifle and machine gun fire, and would leave it at that (they also made tea with the hot water produced off the machine guns, fun fact). The officers had a hell of a time getting them to do much raiding.
Around the time of the Battle of Loos, Graves pretty much gave up on life, and frequently volunteered to go on trench raids at night. I believe this was after he had been transferred to the RWF. He usually took a small squad of men (as to avoid detection) armed with multiple grenades and Webley revolvers. He became pretty good at raids, and mortality rates on his sorties were apparently pretty low. Another book, K-1 the First Hundred Thousand, by Ian Hay, (an excellent read BTW) is about a fictional unit (It’s supposed to be The Argyll & Sutherland Highlanders) fighting in France. It is available for free in many places on line, and discusses trench raiding and its evolution quite a bit (among many MANY other things). Before the advent of more technologically advanced grenades, many soldiers were forced to simply “make do” and used crude substitutes (that were also occasionally furnished by the government) like “jam tin” grenades, which were tin cans stuffed with cordite and a fuse. Better grenades usually meant safer conditions for the ones throwing them, and better results on targets. To try to better answer your question, from what I’ve read, trench raiding evolved pretty extensively during the war, especially in the opening years. If anything, trench raiding quickly became “an art form” (so said Ian Hay, who performed it) and men were self proclaimed “specialists” in what they did – be it throwing grenades, cutting wire, or sneaking around. That being said, mortality and success rates really depended on the circumstances of the fight. Doing a raid during the day, for example was generally a terrible idea. Doing one at night under cover of fog, was a much better one. Having experienced soldiers that had a clear idea of what was going on (and what they should be doing) was an obvious bonus. Just remember to freeze when the flare goes up.