I had the same issue. I mained roam/captain for a long time and struggled with both laning and jungling. Like you said, I’d never really been given the opportunity to play any other roles.
Personally for me, 5v5 has helped a tremendous amount. The current meta with a top, middle, bottom lane, 1 jungle, 1 roam has allowed me to play a lot of different characters. Some of which I’d never thought I’d enjoy.
I have a lot more confidence in my capabilities as a carry now. Here’s a couple suggestions on what helped me progress and expand my versatility:
1)Last hitting
-Inexperienced laners suffer a lot from lack of progression and gold as they transition into the mid and late stages of a game. Match that with an enemy hero constantly on the other side, things can get pretty spicy. It’s always good to have a higher CS score than your enemies, and until you’re getting actively involved in team fights, last hitting should be your priority.
Method
-Before the battle begins, use your first purchases to maximise your damage output. Ex) Ringo paired with 2 weapon blades. This isn’t necessary, but assuming you’re inexperienced, this will help with clearing minion waves and making sure you get that last hit.
-Use your vision objects on places you’re most concerned about getting flanked. Vision is vital!
-Don’t overextend. The long term goal is to make more gold than your opponent. As a beginner, you should try to control the lane by looking for attempts at cleanly hitting your opponent. CLEANLY hitting. Unless you have a distinct advantage, don’t chase the bugger in hopes that you can savour a kill. Just make them feel insecure, and they’ll eventually give you your opportunity to kill them.
-Don’t be afraid to recall. If things don’t go as planned at the beginning, chances are you’ll have minimal damage done to your turret by the time you return. If you don’t want to recall, don’t be afraid to hide behind your turret. You can still last hit most of the minions. Normally, the turret will leave your smaller minions within one hit of your weapon assuming the minion is undamaged. The medium ones will take two turret hits before being within one shot. If you plan on using this tactic, try not to hit the minions beforehand. Or else this is useless.
-Practice! Building muscle memory will make last hitting simple. Eventually, it’ll become common knowledge when you need to hit a minion.
2)Positioning in team fights
-Most games last a while to the extent where you have several tier three items. AKA, the late game.
Method
-A carry normally shouldn’t be the one to initiate a fight. Staying back and trying to pick off weaker opponents OR an opponent most of your teammates are targeting is key. As a major damage dealer, your team relies on your damage output as well as your survival. Let the captain engage, see what enemies are easiest for you to pick off, and attack while staying safe.
-Staying safe is easier said than done. There WILL be people wanting to target you. Your builds should consist of some sort of defence like a reflex block so that you can defend any attempts at putting you into a bad position. Running boots are also recommended for quick escapes. If there’s no hope, those boots can save your life, an ace, and stall your opponents.
-A lot of good positions once again come from learning and experience. I can’t tell you where to go because I have no idea where you might be when a team fight occurs. Just try to understand where your teammates and opponents are at the time of the fight. If you’re being chased, bait the enemy into a teammate. If you’re being an aggressor, try to cut off any easy escapes. Be wary of where an enemy might come from. Try to have vision around where the fight is taking place.
These are just simple things that helped me. Most people probably know about them, but I know how difficult it is to transition from a support into a carry and I personally lacked a lot of these skills. I stopped playing about a year and a half ago and came back just recently, enjoying the game more than ever. I might be a little dull on some of the terminology or current meta, so hopefully someone else can voucher that these things are necessary.
Best of luck! I’m always down to play if you need some visual experience or something.