So what do i do to reduce max hit then thieving?

[Nemerlight]

I got auto eat 1 but it seems anything higher than Man kills me in like 5 minutes if i leave my game

[Oktober12th]

As you get better in the Thieving skill, improve the Mastery on the Thieving target and equip more Thieving gear you can steal more successfully and from higher level targets.

You need some support abilities to really just let it run though. Auto-eat (higher Tier the better) and a higher Hitpoints Skill are pretty much required for idling.

[CODESTA147]

To answer your question there are two things to do if you truly want to grind the thieving skill. First is obviously stealth. The easiest stealth item to get without relying on getting the gloves of silence in combat (from thief monster drop) or agility from obstacle 5 is for sure the thiever's cape from Bandit Thug (Level 12 Thieving) as his perception isn't too high from thieving starting out and as it's an Unique Area Drop and not an NPC or Rare Drop, the rates are much higher.

Now before you try and get the goblin's mask or the sneakers in thieving, I recommend you detour to the second option, and that is reducing damage because you are going to have to waste a lot of rolls to get those to compared to the cape. To reduce damage you have to have the damage reduction stat on your combat status. The easier method is just to waste gold on upgrading steel, mythril or adamant, etc gear to the gold upgrade as only the (G) upgrade of the basic gear have damage reduction which increases as the tier of gear is higher, like dragon gear has 6% Damage Reduction (DR) and one tier lower, the Runic Gear has 5% and so on. Obviously only get the chest, pants, and shield as your easy source of DR. Of course there are better options but if you have them, then obviously you'd have a lot of food by that point and thus wouldn't worry about it.