Anytime a carbocation forms, look to see if it is possible to obtain a more stable carbocation (Tertiary > Secondary > Primary). If it is possible you can perform a hydride shift or methyl shift (NOTE: you can only perform these two shifts if the carbocation is only ONE carbon away from obtaining a more stable carbocation).
Anytime a carbocation forms, you'll get a racemic mixture (ie. the OH can be added on a wedge or dash). This is due to the geometry of the carbocation to be planar, therefore the OH can attack the carbocation from the back (drawn as a dash) or from the front (drawn as a wedge).
The mechanism will be same regardless of what reagent you have. Always start with the H3O+.