First, choose a role that is easiest for you or that you can play without practicing. I can say that the choice of a game role already at the start will weed out a third of unnecessary characters. This will allow you to reduce your views of the characters significantly. It is clear that in present-day Dota, two dozen heroes can be used in different positions. However, you need to practice various characters to make a single hero your signature. That is, any opportunity to reduce the list of heroes will have its result.
Second, it’s recommended to monitor the current situation of the meta-heroes. Undoubtedly, choosing a balanced hero who will not be destroyed in the next patch is essential. Kunkka is almost not touched, probably 10 patches already. And Attacker calmly plays on him at a very high rating.
Third, watch videos of professional Dota 2 players and ranked nerds. Dota 2 is such a popular game that many people earn money. Most of them are YouTubers who make videos with it. Now you can find a lot of channels on which either just publics of pro-players or games with comments are posted. For example, you want to make Wraith King your signature hero. In that case, look for Timado games, as Wraith King is his signature hero. The same can be said about Storm Spirit - Sumail, Invoker - Miracle. You can also find the profiles of these players on the same Dotabuff and independently monitor their games on certain characters.
Maybe not even the way the nerd plays, but even the mistakes made by the enemy, after which the hero destroys his enemy. It is clear that for the skill you need to play well and a lot, but visual memory is also a good thing. You will remember actions, timings, features of movement, etc. It's an exp that you will later be able to implement in your games. But don't “ape” the player's style daily. Create your own individual “dish” that will make you a unique player on your signature hero. For example, if you love to push opponent's towers, Nature's Prophet will suit you because the hero can easily teleport around the map and Split Push.
Moreover, if you need a signature hero for one patch, you can carefully follow the win rates on Dotabuff, as well as the pro-scene and pubs of pro-players. For example, Bane, Marci, Tiny were unbalanced in the last patches. In general, just look at the overall win rate of the character in the games. If it is above 55%, this hero is strong in this patch. Just choose the character that suits your role in the game.
From my point of view, the banalest thing is to play a lot and practice on different heroes until you understand that this or that hero can become "my signature". Of course, playing 10 games a day is the fate of professionals. But 2-3 games a day on one hero is entirely within the power of an ordinary player. I hope the information described above gave results and helped you. Play and choose your hero on which you will be the best player. GLHF!