Actually invading Russia wasn't necessarily against his generals' advice even though there were some who argued for and against it as is almost always the case for operations of that size, (chapter one of 'War of the Century' by Laurence Rees, published by BBC Publications, 1999). During Operation Barbarossa, Hitler personally interrupted the original plan by constantly diverting forces from one front to another multiple times which slowed down the main force, Center Group, that was tasked with capturing Moscow. Also during Operation Blau, Hitler put too much emphasis on the capture of Stalingrad which was originally meant to only help protect the flank of the main force that was advancing into the Caucasus. The number of forces that were diverted to participate in the battle of Stalingrad weakened the flanks enough for the Russians to counter attack across an ill-defended Don River which ultimately lead to the capture of a quarter-million men. From there it was the Soviet's War to lose.

In the later stages of the war when the Germans were on the defensive Hitler opposed all manner of strategic retreat. He saw it as unforgivable cowardice to cede captured territory, even if it had no strategic value and holding it was untenable. This would result in numerous instances of German forces being encircled and captured, causing unnecessary losses to the army. Stalingrad is the most well-known but by no means the only example of this happening.

Worse still, in cases where a retreat was called against Hitler's wishes he would have officers removed from duty or even court-martialled. Heinz Guderian wrote in his memoirs about many cases where he would personally have to interfere as chief of the OKH to save the military careers (or even the lives) of such men.

On a more micro-scale analysis of Hitlers hindrances on the Wehrmacht I would recommend you read: Antony Beevor's - D-Day The Battle for Normandy. There you can see how Hitler interfered with critical military decisions which ultimately helped the allies advance into Europe. Alternatively, Antony Beevor's: Berlin details Hitlers increasing interference with the Wehrmacht towards the end of the war. Very interesting to think what might have happened if he wasn't responsible for so many blunders, although the allies would have certainly won in the end.

I heard some of hitlers early decision-making helped the war effort a lot and was part of the reason why he mistrusted his high command later on. Is this true?

To add to other decisions that have not been mentioned. Hitler reinforced north Africa after the Torch landings, which most likely resulted in the surrender of Arnim and 250,000 troops. He refused to allow panzer divisions to immediately attack Normandy beach head; alot of historians cite this as their only possible chance to stop it. In Norway they left about 10-12 divisions there for no reason; they simply waited out the war and surrendered.