Well if you just started on dota2, denying creeps doesn't really matters.
Lol has zero turn rates and fast attack animation, makes them easy to last hit.
Meanwhile in doto2 every hero have different turn rates, attack animation, and projectile speed so it's normal if you have problems with last hitting on doto.
The average league player, when confronted with turn rates, attack points and projectile speeds, tries to immediately find flaws and label them as dumb or unnecessary. It makes them feel pretty bad being stuck with an average 1 lasthit per minute, despite these players viewing themselves as "experienced in mobas". The best approach when trying to learn DotA properly is to recognize yourself as the shitter you are - it's what I did, playing league for years and once switching to DotA not getting a single lasthit with drow on a freefarm lane. From a DotA perspective league doesn't really have an eco aspect to its laning phase since there's no actual wave control and lasthits can be considered part of the passive income anyway.
Some real good stuff to learn farming properly are botgames. Insane bots deny like assholes and if you pick a hero with low base damage (Quas invoker, Techies) or someone with a horrible attack animation (Zeus, Drow) you'll learn that in some matchups there is actually no way for you to ever get any lasthit numbers-wise and you have to improvise, i.e. timing several creeps to get into lasthit range at the same time to force the opponent to make a decision over deny vs farm, securing at least some creeps that way. There's depth in this part of the game that's not very obvious to beginners, especially coming from a league background where you automatically take every single lasthit as granted and think it's dumb to get starved on your lane.
Farming heroes that have a rather easy time lasthitting include Juggernaut, Anti-Mage, Viper, Tiny and Terrorblade. Supports that have a very easy time denying include Treant (Highest base damage in the game) and Bane (one of the best attack animations in the game, coupled with a damage debuff for the opponent). It's not wrong to avoid heroes you can't farm reliably yet when you're just starting out.
As a guy who oftens switches between the two, take to heart what nacho just said.
DotA is the MOBA of all MOBAs, the one that started it all. Not to mention compared to LoL, SMITE, or any other MOBAs, DOTA2 didn't change any of its mechanics when it was ported to Steam, they actually improved on it. Meaning compared to DotA and all the others, DOTA2 has the hardest gameplay and mechanics to master.
The thing about converting between the two is that it's a lot easier for DotA players to convert to LoL than vice versa, because the mechanics of Dota is practically the same with LoL, only they're more tweaked to be a lot easier than DotA. The same cannot be said for Lol players converting to DotA.
So it's all right to feel like you're shit. We've all been there. I bet you didn't feel like shit in LoL. Because instead of comparing it to DOTA2, you were having too much fun learning all the shit LoL had to offer.
Which is why I offer you this advice: Go in blindly and just enjoy the game from the ground up without comparing it to LoL. After all, everyone always starts incredibly shitty when playing a new game.
PS
The Year Beast Event is freakin awesome (although it had a rocky start due to server issues). I got a lot of new sets, including a Legendary Kunkka and a Mythical Mirana and Sand King set :D
I've got 1200 hours on Dota 2, and I was actually apart of a Gaming Industry tournament that recently ended. I was on the indie dev team "Generic" we ended up getting knocked out by Giantbomb's team "League of Legends" but at least we knocked out EA's team...
Where was I... oh yeah. I've got a lot of hours on Dota 2, maybe a few dozen in League and hundreds in Smite. If anyone wants to play my Steam ID is ChatmanJay! I mainly play support, Enchantress, Chen, Shadow Demon but I'm comfortable in any position(ha) Leave a comment on my steam page if you add me so I don't think you're just some spam bot. GLHF!