For regular travel within London (including the morning peak-fare period) you might need to get an Oystercard AND to put a weekly or monthly Travelcard onto it, rather than using your Oystercard on a 'pay as you go' basis (as you probably would if you were a tourist travelling only at off-peak times). You can also buy both annual and 'odd period' Travelcards.
For example, if you lived in Zone 3 but worked in Zone 1 (travelling there on the Underground) the fares are as follows:
Cash: 2 x £4.80 = £9.60 per day.
Oystercard (using pay-as-you-go): £3.30 to work during peak time + £2.80 to get home off-peak = £6.10 per day.
Oystercard + Weekly Travelcard = £37.70 per week. (Equivalent to £7.54 per day, based upon a 5 day week - but see below).
Oystercard + Monthly Travelcard = £144.80 per week. (Equivalent to £6.90 per day, based upon 21 working days in the month - but, again, see below).
It might seem that using a pay-as-you-go Oystercard is cheapest but any additional travel (such as buses) will be charged for. However, as long as you stay within the inner 3 zones your total payment can't exceed £7.50 per day.
Using the weekly or monthly Travelcards includes unlimited additional travel within Zones 1 to 3 AND (importantly) includes weekend travel as well, so they may well work out cheapest overall.
Map of travel zones:
http://www.emta.com/IMG/pdf/travel_card_zones.pdf
(You'll probably need to hit the 'zoom' button a few times to see the detail.
Fares:
https://tfl.gov.uk/cdn/static/cms/documents/tube-dlr-lo-adult-fares.pdf