We address the problem of optimally identifying all kilonovae detected via gravitational-wave emission in the upcoming LIGO/Virgo/KAGRA observing run, O4, which is expected to be sensitive to a factor of similar to 7 more binary neutron star (BNS) alerts than previously. Electromagnetic follow-up of all but the brightest of these new events will require >1 m telescopes, for which limited time is available. We present an optimized observing strategy for the DECam during O4. We base our study on simulations of gravitational-wave events expected for O4 and wide-prior kilonova simulations. We derive the detectabilities of events for realistic observing conditions. We optimize our strategy for confirming a kilonova while minimizing telescope time. For a wide range of kilonova parameters, corresponding to a fainter kilonova compared to GW170817/AT 2017gfo, we find that, with this optimal strategy, the discovery probability for electromagnetic counterparts with the DECam is similar to 80% at the nominal BNS gravitational-wave detection limit for O4 (190 Mpc), which corresponds to an similar to 30% improvement compared to the strategy adopted during the previous observing run. For more distant events (similar to 330 Mpc), we reach an similar to 60% probability of detection, a factor of similar to 2 increase. For a brighter kilonova model dominated by the blue component that reproduces the observations of GW170817/AT 2017gfo, we find that we can reach similar to 90% probability of detection out to 330 Mpc, representing an increase of similar to 20%, while also reducing the total telescope time required to follow up events by similar to 20%. C1 [Bom, C. R.; Fraga, B. M. 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[Pineda, J.] Millennium Inst Astrophys, Nuncio Monsenor Sotero Sanz 100, Santiago, Chile. [Wiesner, M. P.] Benedictine Univ, Dept Phys, 5700 Coll Rd, Lisle, IL 60532 USA. [Aguena, M.; da Costa, L. N.; Pieres, A.; Santiago, B.] Lab Interinst Eastron LIneA, Rua Gal Jose Cristino 77, BR-20921400 Rio De Janeiro, RJ, Brazil. [Bacon, D.] Univ Portsmouth, Inst Cosmol & Gravitat, Portsmouth PO1 3FX, Hants, England. [Bernardinelli, P. H.] Univ Washington, Dept Astron, Box 351580, Seattle, WA 98195 USA. [Bertin, E.] Inst Astrophys Paris, CNRS, UMR 7095, F-75014 Paris, France. [Bertin, E.] UPMC Univ Paris 06, Sorbonne Univ, UMR 7095, Inst Astrophys Paris, F-75014 Paris, France. [Bocquet, S.; Gruen, D.] Ludwig Maximilians Univ Munchen, Fac Phys, Univ Observ, Scheinerstr 1, D-81679 Munich, Germany. [Brooks, D.; Doel, P.; Swanson, M. E. C.] UCL, Dept Phys & Astron, Gower St, London WC1E 6BT, England. [Carrasco Kind, M.; Gruendl, R. A.; Menanteau, F.] Natl Ctr Supercomp Applicat, Ctr Astrophys Surveys, 1205 West Clark St, Urbana, IL 61801 USA. [Carrasco Kind, M.; Gruendl, R. A.; Menanteau, F.] Univ Illinois, Dept Astron, 1002 West Green St, Urbana, IL 61801 USA. [Carretero, J.] Barcelona Inst Sci & Technol, Inst Fis Altes Energies IFAE, Campus UAB, E-08193 Bellaterra, Barcelona, Spain. [Conselice, C.] Univ Manchester, Jodrell Bank Ctr Astrophys, Sch Phys & Astron, Oxford Rd, Manchester M13 9PL, Lancs, England. [Conselice, C.] Univ Nottingham, Sch Phys & Astron, Nottingham NG7 2RD, England. [Costanzi, M.] Univ Trieste, Astron Unit, Dept Phys, Via Tiepolo 11, I-34131 Trieste, Italy. [Costanzi, M.] INAF, Osservatorio Astron Trieste, Via GB Tiepolo 11, I-34131 Trieste, Italy. [Costanzi, M.] Inst Fundamental Phys Universe, Via Beirut 2, I-34014 Trieste, Italy. [De Vicente, J.; Mena-Fernandez, J.; Rodriguez-Monroy, M.; Sanchez, E.; Sevilla-Noarbe, I.] Ctr Invest Energet Medioambientales & Tecnol CIEM, Madrid, Spain. 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C3 Centro Brasileiro de Pesquisas Fisicas; Centro Federal de Educacao Tecnologica Celso Suckow da Fonseca (CEFET-RJ); United States Department of Energy (DOE); University of Chicago; Fermi National Accelerator Laboratory; University of Michigan System; University of Michigan; University of California System; University of California Berkeley; Universidade Cidade de Sao Paulo; Universidade Cruzeiro do Sul; University of Wisconsin System; University of Wisconsin Madison; University of Queensland; University of Chicago; Consejo Superior de Investigaciones Cientificas (CSIC); CSIC - UAM - Institut de Fisica Teorica (IFT); Autonomous University of Madrid; Stanford University; United States Department of Energy (DOE); SLAC National Accelerator Laboratory; Northwestern University; Northwestern University; Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET); Universidad de Atacama; University of Hamburg; Universidad Andres Bello; Laboratorio Interinstitucional de e-Astronomia (LINEA); University of Portsmouth; University of Washington; University of Washington Seattle; Sorbonne Universite; Centre National de la Recherche Scientifique (CNRS); CNRS - National Institute for Earth Sciences & Astronomy (INSU); Centre National de la Recherche Scientifique (CNRS); CNRS - National Institute for Earth Sciences & Astronomy (INSU); Sorbonne Universite; University of Munich; University of London; University College London; University of Illinois System; University of Illinois Urbana-Champaign; Barcelona Institute of Science & Technology; Institute for High Energy Physics (IFAE); Autonomous University of Barcelona; University of Manchester; Jodrell Bank Centre for Astrophysics; University of Nottingham; University of Trieste; Istituto Nazionale Astrofisica (INAF); Centro de Investigaciones Energeticas, Medioambientales Tecnologicas; Indian Institute of Technology System (IIT System); Indian Institute of Technology (IIT) - Hyderabad; California Institute of Technology; National Aeronautics & Space Administration (NASA); NASA Jet Propulsion Laboratory (JPL); University of Oslo; University of Chicago; University of Pennsylvania; University of Michigan System; University of Michigan; University of Queensland; University System of Ohio; Ohio State University; University System of Ohio; Ohio State University; Smithsonian Institution; Macquarie University; Princeton University; University of Genoa; Istituto Nazionale di Fisica Nucleare (INFN); Universidade Federal do Rio de Janeiro; University of Southampton; United States Department of Energy (DOE); Oak Ridge National Laboratory; United States Department of Energy (DOE); Lawrence Berkeley National Laboratory