When I plan titrations like this, I assume that I will use about half of the graduated buret volume but you could do as Borek suggests and plan to add between 80% to 90% of the buret volume if you wish. You should be using a 50 mL buret so plan on adding about 25 mL of titrant.
You will add an easily measurable amount of peroxide to the erlenmeyer flask and dilute it with some water (100 mL sounds fine). How much H2O2 solution (analyte) you add depends on your glassware. Ideally you would add the peroxide using a Class A volumetric pipette. One or five ml should be appropriate. These are calibrated 'to deliver' (TD) so don't push out the last bit of peroxide that is trapped in the narrow capillary at the tip. (Technique points) Just touch the pipette tip to the inside of the erlenmeyer and let gravity do ALL the work. If you are using graduated cylinders to add the peroxide, use about half of the volume of the graduated cylinder. I would use a 10 mL cylinder filled to 3 to 7 mL (you decide how much). This glassware is calibrated 'to contain' (TC) and so the analyte needs to be quantitatively transferred to the erlenmeyer flask. This involves at least two rinses with water, added to the erlenmeyer each time, to complete the transfer. Add the acid to the flask and begin the titration. Add the acid as a dilute solution (0.1M) to prevent decomposing the peroxide. You will need to determine how much 0.1 M H2SO4 to add from the equation you have. Add about 20% excess acid to this reaction.
In a 20% H2O2 solution, how much (moles) H2O2 do you have? For the "approximate" calculation you can assume a w/v solution. Examine your reaction and determine how many moles of permanganate need to be added to neutralize this. This is the amount of permanganate that should be present in about half of the volume of the graduated buret or 80% to 90% of the buret as Borek suggests. What is this target concentration of permanganate?
Make up APPROXIMATELY this strength of permanganate, ie. use an even number. For example, don't try to make up 0.0483 molar when approximately 0.05 molar will do. Express the concentration to at least 3 significant figures. If you are aiming for 0.05 M, you can express this as 0.0512 M, for example. If you make up one slightly stronger, you will add less during the titration. If it is slightly weaker, you will add more during the titration, no big deal.
Don't forget to do at least three replicates with your analyte and one blank. Blank = water + acid only.
Analyte = 3 - 7 mL H2O2 + water + acid.