Offlane might be one of the trickiest/hardest lanes to play outside of mid (mid usually depends on the hero matchup), because offlane, a lot of times is going against a trilane or sometimes they have to solo lane (not as much now that the meta has changed). Being a good offlaner consists of soaking up experience and finding safe farm when you can. Usually good offlaners consists of heroes with great initiation, or if your team already has decent initiation you can fall more into a utility role and provide team survivability items with items like Hood of Defiance, Crimson Guard, or whatever else your team and could also be good on your hero (always consider what the enemy has as far as lockdown, or magic, or a lot of push, or do you need that extra initiation and Blink Dagger would greatly help). Sometimes you can’t counter the enemies synergy with an item, so you have to choose a good hero that can counter them (for example if they have a push heavy lineup, no item can really counter a heavy push team, you need to pick your hero accordingly).
Make sure at the very start you block the enemy pull camp, this is essential to make sure that the enemy creeps have a higher chance to push into your tower. If you can creepblock and get the enemy’s creeps as close to your tower as possible at the start, even better. When going against a strong lane where it’s hard to stay in the lane, you’re best bet is going to be to deward the highground (the cliff) area next to your tower and usually place a ward on the lowground up on the hill above the neutral camps in the small jungle. When you lane against a hard support they will be doing everything they can to try to find out where you are if you’re not in the lane and they will constantly be dewarding and warding your side of the jungle. It’s very important to control vision on your side of the map, especially if you can’t stay in the lane for very long (that way you can farm the small jungle neutral camps safer).
Once you get some levels (don’t really worry about the items right now, those will come later), usually around level 6 or 7 (if you play a hero that needs an initiation item like Axe who needs blink, it’s ok to farm your item first before rotating around the map), start to rotate around the map when you have your ult. A lot of the offlane heroes in DotA 2 make excellent mid game heroes (Axe, EarthShaker, TideHunter, BatRider, Phoenix, etc). It’s important to utilize their power spike when it’s most effective. Wait until you have your ult and hopefully you can have 3 or 4 levels into another offensive spell and go get some ganks. If you had to build defensively then think first, can you get some kills around the map with just your ult and help from your teammates, usually you can with at least two other heroes helping you.
When you start helping your team get kills, you can start building towards your items that will be most effective to help the team. Remember to ask your teammates to help you gank the enemy safelane, as the enemy safelane will be getting a lot of farm if your supports don’t rotate very often to help your lane out (which happens often in the offlane). Try to make the enemy supports react to your rotations and leave their safelane carry and then if you can, walk back up to your offlane to kill the safelane carry, make sure that you bring a teammate or two if possible (and your ult is back off cooldown). DotA 2 is all about communication and teamwork, and if your teammates won’t help you gank the enemy safelane carry, sometimes it’s best to just go to the jungle and wait for your ult to comeback off of cooldown and gank mid or try once again to get some help from your teammates to gank the safelane carry.
You know who’s good at playing Offlane? The guys at Hero boosting. They are mad good at Dota 2, and I guess it’s natural since they do it for a living. You can check out their Dota 2 boosting services if you’re having a hard time playing the game in ranked. I believe I’ve also recommended their Overwatch boosting in the past, and they are the exact same guys. Mad props to them for what they do, must be a real dream come true.